Primarily designed as a textbook, Trigonometry is a unique treatise on vectors, aiming at providing a fairly complete account of the basic concepts required to build a strong foundation for a student endeavouring to study this subject. The analytical approach to the major theories — Inverse Circular Functions, De-Moivre’s Theorem, Hyperbolic Functions, Gregory’s Series, Trigonometrical Expansions and many more — makes the book highly self-contained and comprehensive guide that succeeds in making the concepts easily understandable. All the elementary principles and fundamental concepts have been explained rigorously, leaving no scope for illusion or confusion. The focus throughout the text has been on presenting the subject matter in a well-knit manner and lucid style, so that even a student with average mathematical skill would find it accessible. In addition, the book provides numerous well-graded solved examples, mostly having been asked in various university and competitive examinations, which will facilitate easy understanding besides acquainting the students with a variety of questions. It is hoped that the book would be highly useful for the students and teachers of Mathematics. Students aspiring to successfully accomplish engineering and also those preparing for various competitive examinations are likely to find this book of much help.