This book aims to provide mathematical analyses of nonlinear differential equations, which have proved pivotal to understanding many phenomena in physics, chemistry and biology. Topics of focus are nonlinear oscillations, deterministic chaos, solitons, reaction-diffusion-driven chemical pattern formation, neuron dynamics, autocatalysis and molecular evolution. Included is a discussion of processes from the vantage of reversibility, reflected by conservative classical mechanics, and irreversibility introduced by the dissipative role of diffusion. Each chapter presents the subject matter from the point of one or a few key equations, whose properties and consequences are amplified by approximate analytic solutions that are developed to support graphical display of exact computer solutions Introduction and preliminaries; Part I. Topological Dynamics: 1. Examples and basic properties; 2. An application of recurrence to arithmetic progressions; 3. Topological entropy; 4. Interval maps; 5. Hyperbolic toral automorphisms; 6. Rotation numbers; Part II. Measurable Dynamics: 7. Invariant measures; 8. Measure theoretic entropy; 9. Ergodic measures; 10. Ergodic theorems; 11. Mixing; 12. Statistical properties; Part III. Supplementary Chapters: 13. Fixed points for the annulus; 14. Variational principle; 15. Invariant measures for commuting transformations; 16. An application of ergodic theory to arithmetic progressions