Fundamentals of Differential Equations by Nagle, Saff and Snider introduces basic theory and applications, exploring modern applications in science and engineering. It can be used with various course approaches (theory, methodology, applications and numerical methods) and used in conjunction with commercially available software. In the 9th Edition, new problems deal with such topics as axon gating variables and oscillations of a helium-filled balloon on a cord. Novel problems accompany the new projects. New examples deal with variation of parameters, Laplace transforms, the Gamma function, and eigenvectors among others. A longer version, Fundamentals of Differential Equations and Boundary Value Problems, 7th Edition, contains enough material for a 2-semester course.