The first half of the second edition of Precalculus: An Investigation of Functions. This is an open textbook, available free online. This first portion of the book (Chapters 1-4) is an investigation of functions, exploring the graphical behavior of, interpretation of, and solutions to problems involving linear, polynomial, rational, exponential, and logarithmic functions. An emphasis is placed on modeling and interpretation, as well as the important characteristics needed in calculus.