This text provides a comprehensive review of the foundations of continuous-time systems, and introduces, with equal emphasis, the “new circuit theory” of discrete-time systems. It looks at the concepts and analysis tools associated with signal spectra—focusing on periodic signals and the Discrete Fourier Transform, and makes students aware of the capabilities of MATLAB. Topics include analysis techniques, frequency response, standard filters, spectral analysis, discrete-time signals and systems, IRR and FIR filter designs, and sampling strategies.