Delay discounting, the process by which remote outcomes decrease in value as a function of delay to receipt, is an area of research at the heart of behavioral economics. Steep delay discounting, or the repeated preference of smaller sooner outcomes over larger later outcomes, underpins many important areas of public health like substance abuse and poor lifestyle choices. Thus, understanding underlying mechanisms and interventions to decrease delay discounting has been a rich line of research of critical importance. Another key area of research within the past few decades has been the search for a quantitative model that best describes the mathematical function of discounting. Early on, economists suggested that discounting followed normative assumptions in economic theory, namely that outcomes would lose value at an exponential or constant rate of decay. However, through extensive empirical research and quantitative comparison techniques, other models favoring a hyperbolic function emerged and are the primary focus of this chapter. At their core, hyperbolic models of discounting assume that outcomes rapidly lose value at short delays and more slowly at longer delays. Hyperbolic discounting is found across multiple species and contexts and accounts for many key findings in delay discounting research. In understanding the form of discounting, researchers are better able to understand the underlying process thereby providing utility for practical application to socially relevant behaviors.