Textbook for MTH 306 at University at Buffalo, State University of New York. This is a derivative work based on Jiri Lebl's Notes on Diffy Q' Differential Equations for Engineers (available at featuring additions by B. Hassard, J. Javor, J. Ringland, and A. Viraj. Chapters 4 and 5 of Lebl's original are omitted from this derivative work.