ENSI oversees and monitors the operation of the nuclear installations in Switzerland. By analysing the reports of the operators, and through inspections and checks, ENSI determines whether the operators are complying with their legal responsibility. It orders all necessary and reasonable measures aimed at preserving nuclear safety and security. In addition, ENSI monitors releases of radioactivity into the environment and the radiation exposure of personnel, attends the annual overhaul shutdowns, assesses incidents, and informs the population about the state of the nuclear installations.

In the event of an incident, ENSI prepares forecasts, ensures that the National Emergency Operations Centre (NEOC) is quickly updated, and advises the relevant authorities on ordering protective measures.

It also drafts directives on nuclear safety and security. Guidelines are enforcement aids that convert legal requirements into concrete terms and facilitate uniform implementation. They also specify the current state of the art of science and technology, including the latest backfitting technology.