This book is written to help students acquire a solid foundation in high school mathematics and enable them to develop problem-solving skills. Considerable effort has been devoted to ensure that the text is understandable and covers areas where learners have common difficulty. Numerous carefully selected examples are provided with detailed solutions to illustrate the mathematical concepts and enhance students understanding of the subject matter. The book has five chapters: (1) Relations and graphs of equations; (2) Functions with emphasis on linear, quadratic, and polynomial functions; (3) Exponential and logarithmic functions; (4) Topics of geometry that are basic to high school; (5) Trigonometric functions, trigonometric equations, and applications involving triangles.Undoubtedly, students who work through this manuscript will find that the book presents a comprehensive foundation to successfully understand high school mathematics. The other book of the author, namely, "Supportive Foundation for Basic Algebra" provides a comprehensive approach to the fundamental concepts and techniques of algebra and offers a useful supplementary background for enhanced mathematical competence.