"Difference Equations, Second Edition" presents a practical introduction to this important field of solutions for engineering and the physical sciences. Topic coverage includes numerical analysis, numerical methods, differential equations, combinatorics and discrete modeling. A hallmark of this revision is the diverse application to many subfields of mathematics. The features include: phase plane analysis for systems of two linear equations; use of equations of variation to approximate solutions; fundamental matrices and Floquet theory for periodic systems; LaSalle invariance theorem; Additional applications: secant line method, Bison problem, juvenile-adult population model, probability theory; appendix on the use of Mathematica for analyzing difference equations; exponential generating functions; and many new examples and exercises.