Impulsive individuals do not consider consequences (information impulsivity) or tend not to wait for future outcomes (temporal impulsivity). Despite costly consequences, might such behaviors be an adaptive response to living in harsh or unpredictable environments? Formal modeling help answer this question by providing clear definitions and cost-benefit analyses across a broad range of environmental conditions. Thus far, formal models exist independently from each other, making it difficult to understand how findings translate to empirical predictions. In this dissertation, I first survey models from diverse disciplines including psychology, biology, management, and economics to develop a conceptual framework of impulsivity. Using this framework, I synthesized results from 30 models to review whether impulsivity is adaptive across a range of environmental conditions. Moreover, I developed two additional formal models that address several important gaps in the literature. The overall conclusion is that impulsive behaviors can be adaptive or maladaptive, depending on the type of impulsivity, harshness, and unpredictability studied. For example, both types are adaptive when individuals are close to a critical threshold, such as bankruptcy, there are few resources (e.g., jobs), or resources that are present now might not be available in the future. They tend to be maladaptive when the quality of resources is unpredictable.