Intraspecific variability in primate vocalizations exists at several levels---within organizational levels of a species, as well as differingly across acoustic variables. This paper reviews signal variability between subspecies, groups and populations, individuals, and within a single individual's vocalizations. The problem of signal variability is best seen when humans describe a species' repertoire. The literature is replete with examples where humans underestimate the amount of variability recognized by the animals; humans typically are lumpers, where playback experiments show that the animals recognize differences that are imperceptible to us. The perceptual cues used by five primate species will have been described. Sensitivity to variability is not uniform between acoustic variables. Variability in signal production has been described for an additional 14 species. Details of interindividual and intraindividual variability of wedge-capped capuchin alarm calls is described. Where early taxonomies of this species' vocalizations recognized two alarm calls, subsequent research by the author described 15 variants of one call, at least three of which were recognized by the monkeys to refer to different objects. The importance of the vocalization's function will be stressed, recognizing that motivational calls may have greater intrinsic variability than those referring to specific external objects.