You cannot conclude unlimited fixed-term employment contracts with an employee! A fixed-term contract will automatically become a permanent employment contract if: More than three successive temporary contracts have been concluded, and/or The total duration of several temporary contracts exceeds a period of three years Interruptions of less than six months between successive temporary contracts are included in the calculation. If there is an interruption of more than six months, a new series will start to run. In the case of a collective agreement, it is possible to deviate from this chain rule.