This chapter explores the powerful consequences of ostracism — being ignored and excluded — at the neurophysiological, emotional, cognitive and behavioral levels. Once ostracized, individuals first recoil in pain, then perceive and respond to their social environments differently, leading them to interpret and attend to particular information that may help them cope, or often, that may perpetuate their state of exclusion. We will discuss the nature and antecedents of adaptive and maladaptive reactions to ostracism. Finally, we will report several experiments aimed at explicating the links between ostracism and pro-social or anti-social behavior.