This is a mathematics textbook that covers mostly precalculus topics with some introductory calculus, as well as more advanced topics that are often not covered by a standard high school curriculum. A chapter proceeds by first establishing some central definitions and then further mathematical consequences, gradually developing the topic from scratch in the process. Unlike many other textbooks in precalculus, this book places emphasis on the art of mathematical proof, with an abundant supply of theorems, lemmas, and other problems that require such proofs. Detailed solutions and proofs are supplied as well.The main purpose is to aid readers who wish to learn precalculus and advanced supplemental topics through a more theoretical and abstract perspective and challenge their mathematical critical thinking skills rather than solve simple computational problems. The book is intended to develop the reader's conceptual understanding of the subject, as well as harness their curiosity in exploring such advanced topics. Furthermore, the book can be used as a supplementary text for students currently taking a precalculus or similar level math class who wish to learn more and go beyond the standard precalculus chapters, and into more abstract, advanced topics that are often not taught in many high schools at all.