This encyclopedia contains trigonometric identity proofs for some three hundred identities. The book is presented in the form of mathematical games for the reader's enjoyment and includes a concordance of trigonometric identities, enabling easy reference. Trig or Treat is a must-have for: ¿ every student of trigonometry, to find the proofs for trigonometric identities that may be set in class or in exams; ¿ every teacher of trigonometry, to have easy access to trigonometric identities of different levels of difficulty, to set assignments for different levels of students; ¿ every library, to provide a ready resource for students ¿ every aficionado of Sudoku, crossword puzzles, jigsaw puzzles, Tetris, and other games, who love an intellectual challenge.