A method for configuring control software in a rail vehicle. The control software, which is designed for a multitude of rail vehicles, implements basic functions that are required for the basic operation of the rail vehicles. The control software additionally implements optional functions required to execute client-specific requests. The specifications, combinations and functional sequences of the basic functions and optional functions are tested, validated, and approved before the functions are implemented in the rail vehicles, whereupon the basic functions and optional functions are made available in the rail vehicles. In a selected rail vehicle, at least one optional function is activated or deactivated using a switching parameter that is individually allocated to the optional function. The switching parameter required therefor is established outside the rail vehicle and is then transmitted to the selected rail vehicle.