Employee ethical behaviors are a frequent topic of business research and a critical criterion for organizations seeking to implement socially responsible, ethical business practices. They, alongside organizational citizenship behaviors and employee green behaviors, reflect one of the three major domains of employee responsible behaviors through which organizations realize corporate social responsibility goals. In this article, we present a critical review of theoretical conceptualizations, taxonomies, and assessment of employee ethical and unethical behaviors. We consider definitional issues and situate the construct of (un)ethical employee behaviors within the current Consensus Taxonomy of Counterproductive Work Behaviors (CT-CWB). We describe the structure and major dimensions of employee ethical behaviors and evaluate the construct coverage, psychometric properties, and shortcomings of major available ethical behavior measures. We provide a brief summary of individual differences determinants of ethical behaviors. We identify important directions for future research and the critical need for more adequate measurement of (un)ethical behaviors.