Employee’s pro-environmental behaviors have long been studied in the environmental management literature; however, this has not been done in a systematic manner. Attempts to provide a suitable definitional framework for this concept are quite recent and mostly based on studies in the field of industrial and organizational psychology. This chapter integrates these two streams of literature, which often tend to overlook each other, in order to shed more light on the nature of employees’ pro-environmental behaviors. Based on a discussion of the existing literature, the chapter highlights the complexity, context-dependency, and multifaceted characteristics of employees’ pro-environmental behaviors and proposes a comprehensive definition that captures the wide scope and diversity of this concept.