Parrots are renowned in captivity for their vocal flexibility, and although studies of avian vocal learning focus largely on songbirds, there is some evidence that the majority of parrots may be more vocally flexible than many members of the songbird order. In addition, unlike the majority of most temperate songbirds, both male and female parrots produced learned vocalizations and often share a repertoire of calls, although anecdotal evidence from pet owners suggests that males may be the more vocally flexible sex. However, most of what we know about parrot vocal flexibility and sex differences in parrot communication comes from anecdotal evidence and very limited lab studies that have difficulty mimicking natural parrot social conditions. Thus, the purpose of this work was to investigate how wild parrots are using vocal flexibility during interactions with conspecifics, and how sex differences in communication are expressed in vocal interactions in general and vocal flexibility in particular. I studied two geographically and phylogenetically distant parrot species, the Australian galah (Eolophus roseicapillus) and the neotropical orange-fronted conure (Aratinga canicularis) to address these issues. I conducted four playback experiments either to wild, free-ranging individuals or to wild-caught captives held temporarily in aviaries. Two of these experiments address how parrots are using and interpreting rapid, short-term vocal flexibility during their interactions and how this differs by sex. The other two experiments address more broadly how male and female parrots respond to male and female affiliative and aggressive calls. This thesis demonstrates that in at least two species of parrots, males and females differ in how they rapidly modify their vocalizations during interactions with conspecifics. Despite sharing a repertoire of calls, both galahs and orange-fronted conures distinguish the sex of a caller based solely on acoustic cues, and males and females interact differently with conspecific callers, suggesting that the sex of interactants is a highly relevant factor even during interactions that do not seem to be primarily for the purpose of mate attraction. These experiments begin to shed light on the incredible intricacies of flexible parrot vocal communication.