These materials, which have been developed and thoroughly class tested over a period of several years by the authors, are intended for use in courses in differential equations taught at the sophomore/junior level in American colleges and universities. Prerequisites for using these materials is the calculus of one variable, although calculus of several variables, and linear algrbra, are recommended. The text covers the standard topics in first and second order equations, power series solutions, first order systems, Laplace transforms, numerical methods and stability of non-linear systems. For historical completeness, the authors have also included the solution methods of Bernoulli, Clariaut, and Lagrange, if instructors wish to cover them. Liberal use is made of programs in Mathemtica, both for symbolic computations and graphical displays. The programs are described in separate sections, as well as in the accompanying Mathematica notebooks. The book has been designed so that it can be read with or without Mathematica and no pre-requisite knowledge of Mathematica is required to use the book, not to deal with the Mathematica programs contained in ODE.m, the special Mathematica software package residing on the CD-ROM accompanying the text. ODE.m enables students to solve differential equations, much as a calculator would. The CD-ROM, in addition to containing ODE.m, also contains the Mathematica solution of worked examples, the Mathematica solution of exercises, a protrait gallery of some 48 mathematicians who have contributed to the field of differential equations, a selction of various Mathematica noteboosk, Mathematica movies and sample labs for students.