This chapter considers what ethicists say normatively about deception in negotiation, and what social scientists report empirically about the causes, forms, and consequences of deceptive behavior. Following brief definitions of lying and deception, we describe normative approaches found in the business ethics literature that address negotiator bluffing. We then summarize empirical social science research on deception, highlighting work in social psychology and communication theory on lying and its detection. A discussion of (mainly) empirical work on deceptive behavior in negotiation follows, including informational forms of deceptions as well as strategic simulation or suppression of emotions. A concluding section highlights four research needs: greater methodological variety, more focus on cultural context, expanded attention to moral psychology, and better integration between normative and social scientific perspectives.