Staff members, irrespective of their category (A, B, C or L), are usually appointed for an initial period of four years, subject to a satisfactory probationary period of six months.

Extensions for B and C category staff are for an indefinite period and extensions of contracts for A and L grade staff are normally for a period of six years, with a possibility of another extension for an indefinite period. For staff with an indefinite contract, the contract terminates at the end of the month in which the staff member turns 63 if recruited after 1 July 2010.

Different rules apply for Canadians, as Canada is a cooperating country, and in the rare instances where ESA employs nationals of non Member States. In these cases the initial four-year contract can be extended for six years, with further extensions for periods of not more than four years up to the age of 63 if recruited after 1 July 2010.

Some ESA staff positions are referred to as Advance Recruitments. Contracts for advance recruits are for a maximum of two years and are not renewable. However, upon termination of an advance recruit contract an ESA staff contract may be given.