This book focuses on nonlinear investment strategies based on a quantamental approach: a combination of quantitative and fundamental analysis. The natural world, and everyday life, are full of nonlinear relationships. Before introducing nonlinear investing and the quantamental approach, we begin by discussing the fundamental role of nonlinear relationships in two of the greatest discoveries about the nature of our universe: Newton’s law of universal gravitation and Einstein’s theory of relativity. From there, we turn to examples of nonlinear relationships that we can observe in everyday life, and then consider an example of a nonlinear pricing relationship in the US public equity market. After discussing these examples, we define nonlinear investing and the quantamental approach and present the rationale for applying the quantamental approach to nonlinear investing. It should be stressed that quantamental as a methodology can be applied to both linear and nonlinear investing, but the complications and challenges of nonlinear investing make a quantamental approach especially crucial. We conclude by outlining the organization of the book.