You should be prepared for: an individual interview with a recruitment officer, an interview with a panel of staff members capable of evaluating your technical skills and personality, and, possibly, depending on your professional field, a simulation exercise and/or meetings with others involved at the Institute.
We will be trying to understand and assess your current and potential skills, your character and values, how you function and interact with others, and your level of motivation.
You can find advice on this process here.