This textbook covers the fundamental concepts of calculus, knowledge essential for all calculus courses (e.g. Calculus I, Calculus For Science I), as well as other courses (e.g. Mathematics for Science I) taught at Thammasat University and other universities. The text aims to build up the subject in a manner such that solutions to problems is, if not straightforward, then at least greatly simplified by newly-available techniques. Where applicable, different frameworks may be provided for varying use-cases, such as the multiple expressions of the Intermediate Value Theorem, each with their own advantages.