With the presentation at an introductory level, the third edition of the book (2007 copyright) contains a comprehensive treatment of continuous-time and discrete-time signals and systems, with demos on the textbook website (http://users.ece.gatech.edu/~bonnie/book3), data downloaded from the Web, and illustrations of numerous MATLAB commands for the solution of a wide range of problems arising in engineering and in other fields such as financial data analysis. The book contains a large collection of examples and problems, and practical applications that use actual data dowloaded from the Web. It is shown how data can be downloaded and then imported into MATLAB for analysis by techniques covered in the text. Applications include data analysis in the presense of noise, with the focus on filtering noisy signals and the use of the discrete Fourier transform (DFT) to extract the dominant cyclic components of a signal (time series) from noisy measurements of the signal.