GUICS: A Generic User Interface for On-Farm Crop Simulations As knowledge of crop growth and development is quantified, it can be included in the computer code of crop simulators that mimic the essential features of plant–soil–atmosphere–management interactions. The next step necessary is to provide tools to simplify operation of the crop simulator by end users. Our objectives were to (i) develop a graphical user interface (GUI) specifically oriented to on-farm use and (ii) research the possibility of building a generic GUI that could be used with many crop simulators not necessarily having the same structure of input data. We call the interface GUICS (standing for Graphical User Interface for Crop Simulations). GUICS is built on the usability paradigm developed by software designers and has a user-centered design based on results of human–computer interaction interface development lies in human–computer interaction studies. The usability of the interface is facilitated with special features that enhance the directness, user-in-control, consistency, forgiveness, feedback, and simplicity of the interface. Including a simulator in GUICS is a straightforward operation that does not require changes in the simulator code. The GUICS prototype was evaluated by its future users in interviews during which they had hands-on experience. Two years of on-farm use of GUICS has proved the usability of the interface.