Book Description: 'Trigonometry: Functions and Applications' is designed for a two-quarter course at the highs school or college level. This approach imparts theory and applications in a realistic way. Students must 1) Define the function 2) Draw a representative graph 3) Figure out properties of the class of function 4) Use that kind of function as a mathematical model. Therefore, rather than simply seeing graphs of periodic phenomena, the students are expected to draw the graphs themselves. Then they must write equations for the graphs, and use the equations to make predictions and interpretations about the real-world situation they are modeling. The materials are designed to interface well with algebra studied form the functions standpoint. However, since many students have studied algebra from more traditional texts, it has not been assumed that the students have used this approach before the present trigonometry course. It is assumed that the students have studied geometry, and at least on3 semester of high school second year algebra.