In this lecture, the basic methodology of digital filter design software will be reviewed. A number of well-known filter design methods will be covered, but the emphasis will be on using the methods more than deriving them. For most filter design methods, there are usually several software implementations, but this presentation will use the MATLAB functions as examples. The lecture will include examples of using MATLAB to design IIR and FIR digital filters (hopefully with some movies). The classical problem of matching a desired magnitude will be discussed, and then methods that do the total design of both magnitude and phase specs will be presented.