Since its inception at the Institute of Optics at the University of Rochester, the software written by Doug Sinclair has played a key role in the teaching as well as in the performance of optical design. So OSLO, perhaps more than any other optical design software, shows signs of its origins in a teaching establishment. The flexibility of the user interface, the open source nature of much of the code, the CCL programming language which is very similar to C, and real capability of OSLO-EDU, the free version of OSLO, to carry out real design tasks, make it the ideal choice for the teaching environment.