The Schengen Agreement and Acquis: History, Legal Basis, and EU Integration

The Schengen Agreement is the 1985 treaty by which five European states committed to the gradual abolition of checks at their common borders, later implemented by the 1990 Convention and integrated into EU law by the Treaty of Amsterdam. It is the legal point of origin for today’s border-free Schengen framework, distinct from the “Schengen Area” itself.

A Brief History

At a glance, the following timeline highlights the key milestones in the development of the Schengen Agreement and its progressive implementation:

• January 2025: Bulgaria and Romania officially became full members of the Schengen Area, with land border checks lifted.
• March 31, 2024: Bulgaria and Romania partially joined, lifting border checks for air and sea travel.
• January 2023: Croatia joined as a full Schengen member.
• December 2011: Liechtenstein abolished internal border controls.
• 2008–2009: Switzerland abolished land (2008) and airport (2009) border controls.
• 2007–2008: Major expansion included abolition of land, sea, and later air border controls for new EU members.
• 2001: Denmark, Finland, Sweden, Norway, and Iceland joined Schengen.
• 2000: Greece implemented Schengen rules.
• 1997: Italy and Austria abolished internal border controls.
• 1995: First practical implementation: seven states abolished internal border checks.
• 1990: Convention implementing the Schengen Agreement (CISA) signed.
• 1985: Schengen Agreement signed by France, Germany, Belgium, Luxembourg, and the Netherlands.
• 1984: France and Germany first proposed free movement at the European Council in Fontainebleau.

This timeline serves as a chronological guide. The sections that follow provide detailed legal and political context for each stage of Schengen’s evolution.

Legal Basis

The Agreement was signed on 14 June 1985 near the village of Schengen, Luxembourg, by Belgium, France, Luxembourg, the Netherlands and the Federal Republic of Germany. It set out a phased approach to removing internal border checks and called for strengthened external-border controls and enhanced police and customs cooperation. The Agreement was concise and political in character; detailed operational rules followed in the 1990 Convention implementing the Schengen Agreement (CISA).

From Political Commitment to Operational Law: The 1990 Convention

On 19 June 1990, the original signatories concluded the Convention implementing the Schengen Agreement. CISA transformed the 1985 political commitment into an operational legal framework: it abolished internal border checks between contracting parties, introduced common rules for short-stay visas, created the Schengen Information System (SIS), and laid down machinery for cross-border police and judicial cooperation (including provisions on surveillance and hot pursuit).

Entry Into Force and First Implementation (1995)

After technical and legal preparations in the early 1990s, Schengen rules were first applied on 26 March 1995. Checks at internal borders ended among the initial applying states (including the original five plus, by then, Spain and Portugal), with further accessions following.

Integration Into EU Law and the “Schengen Acquis”

Although negotiated outside the European Communities, Schengen became integral to the single market and free-movement project. The Treaty of Amsterdam (entered into force 1999) incorporated the “Schengen acquis” into EU law. That acquis comprises the 1985 Agreement, the 1990 Convention, subsequent accessions and Executive Committee decisions. EU institutions and the Court of Justice thereafter gained competence over Schengen measures, and differentiated participation (opt-outs/opt-ins) was formalised via protocols.

What Is the Schengen Acquis?

The term Schengen acquis refers to the entire body of rules, decisions, and obligations that govern the functioning of the Schengen framework. In EU legal language, “acquis” denotes the accumulated legislation, case law, and practices that Member States are obliged to adopt. For Schengen, this acquis includes:

• The 1985 Schengen Agreement and the 1990 Convention implementing it (CISA).
• All subsequent protocols, accessions, and related agreements extending Schengen to new states.
• Decisions adopted by the Schengen Executive Committee prior to Amsterdam (1999).
• EU legislation that codifies and develops Schengen rules after Amsterdam, including the Schengen Borders Code, the Visa Code, and reforms to the Visa Information System (VIS).

Once incorporated into EU law by the Treaty of Amsterdam, the acquis became binding on nearly all EU Member States, subject to defined opt-outs. Candidate countries for EU accession are also required to accept and implement the Schengen acquis as a precondition for joining the Union.

Evolution of the Schengen Acquis

The acquis is not static. It has developed over time, moving from a set of intergovernmental agreements to a codified and enforceable body of EU law. The following table illustrates its main stages:

Through this layered evolution, the Schengen acquis has become one of the most important components of the EU legal order, balancing free movement with security, border management, and judicial cooperation.

Who Must Adopt the Schengen Acquis?

The Schengen acquis applies differently depending on the category of state. While all EU Member States are legally bound to adopt it, the extent and timing of application vary. Associated non-EU countries also implement the acquis by agreement. The following table summarises the obligations:

This structure ensures that the acquis is uniformly applied across participating states, while allowing for limited exceptions and transitional arrangements. Adoption of the acquis is a legal precondition for joining both the European Union and the Schengen border-free area.

What Schengen Is Not: Distinction From the Schengen Area and Schengen Visa

For clarity, the treaty framework (Agreement + Convention + acquis) should not be conflated with:

• The Schengen Area, which is the geographic space in which internal border checks are lifted in practice.
• Short-stay visa practice or application procedures, which are governed by later EU legislation (notably the Visa Code).

This article focuses on the treaty architecture; operational visa matters are addressed in dedicated legal acts and are outside scope here by design.

Core Legal Mechanisms Created by the Agreement/Convention

1) Abolition of checks at internal borders

CISA’s principal innovation was to substitute internal controls with shared rules, risk-based policing, and mutual assistance. The end of systematic passport checks at internal frontiers was paired with safeguards, including the possibility to reintroduce internal controls temporarily under defined conditions (now governed by the Schengen Borders Code).

2) Common approach to short-stay visas

Schengen created the basis for a single short-stay visa valid across participating states, later codified by the EU’s Visa Code, which sets procedures and conditions for short stays of up to 90 days in any 180-day period.

3) Police and judicial cooperation

CISA established cross-border investigative tools and information exchange channels. These provisions were the operational complement to lifted internal checks, ensuring authorities could cooperate when mobility increased.

4) The Schengen Information System (SIS)

SIS was created as a shared alert and information platform to support border, police and judicial authorities. It underpins checks at external borders and police work within the territory, complementing visa and border legislation adopted later at EU level.

EU Codification After Amsterdam: Principal Regulations Linked to Schengen

After integration into EU law, key Schengen-related rules were codified and updated through EU regulations:

• Schengen Borders Code (Regulation (EU) 2016/399) sets the rules for crossing external borders and the conditions and procedures for any temporary reintroduction of internal border control.
• Visa Code (Regulation (EC) No 810/2009) establishes the procedures and conditions for issuing short-stay visas, including the standard validity concept “90 days in any 180-day period.”
• Visa Information System reform (Regulation (EU) 2021/1134) updates the data architecture supporting the visa process, extending checks and interoperability to reinforce security while facilitating uniform practice.

Institutions Supporting the Schengen Framework

The operation of Schengen is supported by several EU institutions and agencies:

• European Commission: Oversees the correct application of the acquis and issues reports under the Schengen evaluation mechanism.
• Frontex (European Border and Coast Guard Agency): Coordinates joint operations and assists Member States at the external borders, especially under pressure.
• eu-LISA: Operates the large-scale IT systems central to Schengen, including SIS, VIS, Eurodac, and the upcoming Entry/Exit System (EES) and ETIAS.

Differentiated Participation: Opt-Outs, Opt-Ins and Association

When the Treaty of Amsterdam entered into force on 1 May 1999, the Schengen acquis was incorporated into EU law. But it wasn’t straightforward. A system of differentiated participation emerged – essentially, not all EU Member States had to apply the acquis the same way. Some states got opt-outs through Protocols attached to the Treaty. Others could participate in specific areas only (police and judicial cooperation, for instance). And agreements were made to associate non-EU countries with Schengen too.

United Kingdom

The UK used its opt-out from abolishing internal border checks. Under the Amsterdam Protocol, it could request to participate in individual Schengen measures – and it did. The UK government took part in various provisions on police & judicial cooperation. But it never joined the border-free zone itself. Passport controls stayed in place for travel between the United Kingdom and Schengen countries. This continued right until the UK withdrew from the European Union.

Ireland

Ireland opted out of full participation as well. Why? Mainly because of the Common Travel Area with the United Kingdom; both governments wanted to keep this arrangement. Ireland does participate in quite a few Schengen provisions though – the ones relating to police and judicial cooperation. Like the UK, Ireland didn’t remove checks at borders with the Schengen area.

Denmark

Denmark’s situation is different. It’s bound by the Schengen acquis under international law, but its Protocol lets it decide case-by-case whether to apply new measures adopted in the EU framework. Denmark participates fully in the original Schengen setup. Later developments though? Those need separate parliamentary approval.

Associated non-EU countries

Norway and Iceland got associated with Schengen through agreements in the late 1990s. Switzerland signed its agreement in 2004. Liechtenstein followed in 2008. These 4 non-EU countries implement the acquis fully and they’re part of the border-free area. They help with governance and decision-shaping – but no voting rights in EU institutions.

Recent accessions

New EU member states have to join Schengen once they’re technically ready – it’s required by the Treaties. Croatia joined fully on 1 January 2023. Bulgaria and Romania had been applying parts of the acquis for years; they finally became full members on January 1, 2025, lifting all internal border checks. Cyprus? It’s legally obliged to join but hasn’t been admitted yet. Technical and political conditions are still being reviewed.

Enlargement and Progressive Application

The Schengen Agreement (originally signed by just five states in 1985) has expanded quite steadily over four decades. The pattern for enlargement has stayed basically the same: new EU members have a legal obligation to join, there’s a technical evaluation of readiness, then existing members give unanimous political approval. This gradual approach turned what was a small intergovernmental initiative into one of the largest border-free zones worldwide.

Initial implementation (1995)

Seven states formally abolished internal border checks on 26 March 1995. These were Belgium, France, Germany, Luxembourg, the Netherlands, Portugal & Spain. Italy and Austria joined in 1997 – the first real enlargement beyond founding members.

Early 2000s expansion

Greece implemented the acquis in 2000. Then in March 2001, Denmark, Sweden and Finland joined. Norway and Iceland came in as associated states at the same time. This pushed Schengen into northern Europe. And it showed non-EU countries could participate fully too.

2004 EU enlargement and Schengen accession (2007-2008)

The big EU enlargement of 2004 brought in ten new Member States. Most implemented the Schengen acquis in December 2007 – that’s when land and sea borders opened. Air borders came later, March 2008. The countries were Czech Republic, Estonia, Hungary, Latvia, Lithuania, Malta, Poland, Slovakia, and Slovenia. It was the biggest single wave of Schengen enlargement ever.

Later enlargements

Switzerland joined (as an associated state) in December 2008; Liechtenstein in 2011. Croatia joined the EU in 2013 but only completed the evaluation process and entered Schengen on January 1, 2023. Bulgaria and Romania finally lifted all internal border checks on 1 January 2025. Cyprus is legally committed to joining but it’s still outside the border-free area – technical and political criteria haven’t been met yet.

The whole system has grown remarkably. From five countries meeting in a Luxembourg town to sign an agreement in ’85, to today’s expansive zone covering most of Europe. Each expansion brought its own challenges. Some took years longer than expected (Bulgaria and Romania). Others went surprisingly smoothly. But the core principle stayed consistent – countries join when they’re ready, and when everyone agrees they’re ready.

The technical evaluations are thorough. Really thorough. Border management systems, document security, visa procedures, data protection… everything gets checked. The SIS (Schengen Information System) connection has to work perfectly. Police cooperation mechanisms need to be in place. And then there’s the political dimension – every single existing member has to agree. One “no” and you’re waiting another year. Or five. Or in Bulgaria’s case, eighteen years.

Each enlargement has required detailed technical evaluations, including assessments of external border management, visa issuance procedures, data protection, and law enforcement cooperation. Only when these standards are met can new members fully lift internal border checks.

Temporary Border Controls and Derogations

The abolition of internal border checks was never meant to be absolute. Never was. From the beginning – the 1990 Convention implementing the Agreement, then later the Schengen Borders Code (Regulation (EU) 2016/399) – they built in escape valves. Countries could temporarily bring back internal border controls in exceptional circumstances. It’s a balancing act: free movement on one hand, public policy, internal security and public health on the other.

Monitoring Compliance with the Schengen Acquis

Since 2013, member states applying the Schengen acquis get evaluated regularly. Council Regulation (EU) No 1053/2013 set up the system. There are on-site inspections, peer reviews by experts from the Commission & Member States. The whole thing. They check if national authorities are correctly implementing Schengen rules – borders, visas, police cooperation, data protection.

Find problems? States have to adopt corrective action plans. Then there are follow-up reviews to make sure they actually fixed things. It’s pretty thorough.

Legal basis

Article 23 of the Schengen Borders Code (that’s Regulation (EU) 2016/399) lays out the conditions. Internal border checks can come back temporarily but only if they’re necessary and proportionate. And only for the period strictly required – though “strictly required” gets interpreted rather flexibly sometimes.

States must notify European institutions and neighboring states about these measures. In theory. The notification requirements are clear enough, but enforcement? That’s another story.

Examples of application

• Terrorism and security threats: Following the 2015 terrorist attacks in Paris, France reintroduced controls at its internal borders, with periodic extensions notified under EU law.
• Migration pressures: During the 2015–2016 migration crisis, several Schengen states temporarily reinstated checks in response to irregular migration flows.
• COVID-19 pandemic: In 2020, the European Union decided to close all Schengen borders temporarily, initially for a 30-day period, before coordinated reopening was managed in stages.

These measures did not alter the fundamental premise of Schengen. They remain strictly regulated exceptions, rather than a return to permanent internal border controls.

These derogations confirm that while the Schengen framework creates an area without internal border controls, it also embeds mechanisms for proportionate, temporary restrictions when serious threats arise. Such measures must be notified to the European institutions, are subject to time limits, and are reviewed for compliance with the proportionality principle. For monitoring current developments and recent notifications of temporary controls, reference should be made to official updates and specialised reporting on Schengen policy [latest Schengen news].

The Schengen acquis and EU regulations

The Schengen Agreement and Convention created the initial framework. Since it was incorporated into EU law in 1999, the acquis has developed through various regulations adopted by EU institutions. The main instruments include:

• Schengen Borders Code (Regulation (EU) 2016/399): This establishes rules for external border checks, defines travellers’ rights, and regulates conditions for temporary internal border controls.
• Visa Code (Regulation (EC) No 810/2009): Sets out the procedures and conditions for issuing uniform short-stay visas – these are valid for up to 90 days in any 180-day period.
• Visa Information System reform (Regulation (EU) 2021/1134): Updates the VIS to improve security, expand biometric use & ensure interoperability with other EU databases.

Together these instruments ensure the principles of the Schengen Agreement are maintained through detailed, uniform and enforceable rules across all participating states. That’s the idea anyway.

Beyond binding legislation, the acquis gets shaped by institutional practice too. The European Commission publishes “State of Schengen” Communications annually, assessing performance and proposing reforms. The Council adopts Conclusions regularly – these set strategic guidance on border management, migration, internal security priorities for the Schengen cycle. It’s an ongoing process, basically.

The whole system keeps evolving. New regulations update old ones. Court rulings clarify ambiguities. Member states push for changes when things aren’t working. And of course, crises (migration surges, terrorist attacks, pandemics) drive urgent reforms that sometimes stick around longer than intended.

Criticism and debates

Schengen gets called one of the EU’s biggest achievements. But it’s taken plenty of criticism too.

• Security concerns top the list. Critics say no internal borders means criminals and terrorists move around undetected. Supporters point to enhanced police cooperation & the SIS database. Whether that’s enough? Depends who you ask.
• Migration pressures test the system regularly. 2015 was rough. Every surge brings the same demands – stricter external borders, burden-sharing, reforms. The usual.
• Public health – COVID showed how fast things unravel. Member States ditched free movement overnight in March 2020. “Temporary” suspension, they said. Some borders stayed closed for months.

It’s always been about balancing freedom with security. Every terrorist attack brings calls to “fix” Schengen. Every migration wave tests external borders. Every pandemic? Borders slam shut first, questions later.

But here’s the thing – nobody seriously proposes scrapping Schengen entirely. Even harsh critics just want reforms. Once you’ve lived without border checks, going back seems medieval.

Read also: Benefits of the Schengen Area: A Comprehensive Analysis of Europe’s Bold Experiment in Transnational Integration

Present and Future Reforms

On 2 June 2025 the European Commission presented its latest State of Schengen Report, which sets out priorities for maintaining and strengthening the Schengen framework. These priorities are regularly discussed by the Council of the European Union and followed up by national administrations. The main areas currently under reform are digitalisation, security, and crisis management.

Digitalisation

The roll-out of new IT systems is one of the most important reforms. The Entry/Exit System (EES) and the European Travel Information and Authorisation System (ETIAS) are due to become operational in 2025. These systems, together with the modernised Visa Information System (VIS), will be interconnected so that border authorities can consult information once instead of carrying out several separate checks. This interoperability is required under Regulation (EU) 2019/817.

Security

The Schengen Information System (SIS) has already been expanded with new categories of alerts and biometric data. The aim is to reduce cases of identity fraud and improve cross-border police cooperation. In practice, this means that police officers and border guards can verify identity documents more quickly and with greater reliability. Member States have repeatedly underlined in Council debates that this is essential if free movement is to be preserved.

Resilience

The COVID-19 pandemic showed that Member States may reintroduce internal border controls suddenly and for long periods. To prevent uncoordinated measures in the future, the Commission has proposed clearer rules for derogations under the Schengen Borders Code (Regulation (EU) 2016/399). The Council has supported these efforts in its Conclusions of 13 June 2024, calling for more transparency and regular reporting when internal controls are prolonged.

Interoperability of EU Information Systems

By mid-2026, SIS, VIS, EES, ETIAS and Eurodac are expected to operate on the basis of a single interface. This change is being implemented by the EU Agency eu-LISA, established under Regulation (EU) 2018/1726. Border guards will then receive a single response when checking travellers, rather than having to query several systems separately. The reform should make border checks faster and reduce the risk of errors.

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