Written in a modern and easily understandable style, this introduction to linear systems combines mathematical precision, technical detail and sound pedagogy. Discrete and continuous ideas are developed in parallel, taking advantage of the similarities between these two representational modalities. Sections on the Fast Fourier Transform and its applications introduce the reader to modern techniques of considerable interest. The final chapter, on state variables, with particular attention given to application in control theory, employs previously introduced concepts and functions as a capstone chapter in the study of linear systems. Numerous drill problems and worked examples reinforce basic techniques.