This textbook introduces readers to the mathematical topics fundamental for the study of economics through a combination of formal definitions, theorems, and proofs, including intuitive and easy-to-follow explanations and visualizations. Its goal is to help students understand the underlying concepts and develop an intuitive understanding of each notion, conclusion, and method presented, supported by formal proofs and approximately 270 worked-out examples. After covering these formal definitions and theorems, the book uses plain language and numerous illustrations (including visual and step-by-step examples) to clarify them and to hone readers' problem-solving skills. Additionally, it demonstrates how these concepts and mathematical methods are applied in economics, highlighting their relevance. It contains a set of theoretical questions and practice problems with solutions at the end of each subchapter. The book is useful not only for undergraduate students, but also for graduate and PhD students, early-career researchers, and any academic who would like to review, strengthen, and consolidate knowledge and skills, and become a powerful researcher.