In 2025, we will celebrate the 40th anniversary of the signing of the Schengen Agreement, which gave its name to an area that today covers more than 4 million square kilometres and is home to almost 420 million people. The Schengen area is considered one of the most important achievements of European integration. Its essence is the effective control of persons crossing external borders and the integrated management of external borders, as well as the absence of any controls on persons crossing internal borders, regardless of their nationality. However, states still have the right to unilaterally reintroduce border controls temporarily in exceptional situations. This possibility has been used by many states, especially when faced with migration and health crises. The article aims to show how the interpretation of the existing rules on the temporary reintroduction of border controls has changed in the face of these crises, and how the rules have been amended.