Signals and Systems is a course that covers the basic concepts of both continuous-time and discrete-time signals and systems. The course explores signal and system representations in both time and frequency domains, and their relation through the Fourier transform and its generalizations. The course also covers filtering and filter design, modulation, and sampling for both analog and digital systems, as well as feedback systems for both analog and digital systems. The course is taught by Alan Oppenheim and is available on MIT OpenCourseWare.