First, you must sign a so-called hosting agreement (or a contract) with a research organisation, such as a university, a research institute or a company. This hosting agreement establishes that a valid research project exists and provides some relevant information (dates or duration of the project, area and title, etc.).
You must also have the following documents:
- a valid passport or another travel document,
- proof that you will have enough financial resources to cover your living costs during your stay, as well as your return travel costs,
- health insurance.
Depending on the EU country, you may also be asked to submit the following documents:
- proof that you have paid an application fee for the processing of your application,
- a written promise from the research organisation that it will reimburse any costs to the Member State if you stay longer there than allowed by your permit.
For more details, please check the page related to researchers of each Member State.