Both acute and chronic psychological and social stresses can impair reproductive hormone secretion in a variety of nonhuman primate species. This impairment can be subtle, consisting of a mild suppression in reproductive hormone secretion, or dramatic, underlying a complete suppression of fertility and reproductive behavior. Although group mean responses to various stresses can be measured, it is clear that there are marked differences in the response of the reproductive axis to these stresses among individual animals. Factors that contribute to the variability in the response of the reproductive axis include the type of stress, the magnitude and duration of stress, the perception of the stress by the individual, the social status of the individual, the concurrent level of aggressive behavior displayed by the individual, seasonal cues, and the prior level of activity within the reproductive axis. During some stresses, activation of the adrenal axis, endogenous opioid pathways, increased prolactin release, and changes in sensitivity to gonadal steroid hormone feedback appear to play a role in mediating the effects of behaviorally induced stresses on the reproductive axis. However, a great deal more work is needed to understand the mechanisms underlying impairment of the reproductive axis by most psychological and social stresses, as well as the mechanisms underlying differences in susceptibility to stress-induced impairment of reproductive function within individuals.