This book is the first to offer a systematic methodology for solving nonlinear ordinary differential equations (ODEs) using power series, specifically those arising in mathematical physics. It provides tools to eliminate the tedious manipulation of infinite series, enabling recursive computation of all terms. The authors also present a structured approach to overcoming convergence issues inherent to such methods, demonstrating that power series solutions can be both accessible and practical. The authors' teaching philosophy - that mathematics is best learned by doing - is reflected throughout, with the text largely composed of idea-driven examples and physically motivated problems from their own research. Proofs are included only when necessary for readers to construct custom theorems or definitions relevant to real-world applications. Ultimately, the book shows that power series methods can effectively complement numerical techniques, offering applied mathematicians a powerful and versatile toolset.