Introduction to Operating Systems takes a top-down approach to the teaching of operating systems starting with what the student already knows - the GUI desktop. It covers in depth the major features of modern operating systems, with particular emphasis on Windows and Linux as sources for examples, but avoids any focus on older systems which are now only of historical interest. The treatment is concise, non-mathematical, and with examples drawn from real systems. No prerequisite knowledge is assumed other than a general knowledge of programming.