-The aggressive and courtship displays and vocalizations of the male Anna’s Hummingbird (Culypte anna) are described in detail, and various types of evidence and observations are used to reconstruct the typical courtship sequence. Initial contact is made by the female flying to the male’s territory and attempting to feed; she may have previously visited several other territories in order to evaluate territory quality. The well-known dive display is an aggressive maneuver by the male, although it may play a role very early in the courtship sequence. Following a lengthy chase towards the female’s nesting area, she alights low in dense vegetation. The male then gives the displays most critical for courtship: a back-and-forth “shuttle” display and high-intensity song. These hitherto undescribed displays occur immediately preceding copulation, and are probably the most important isolating mechanisms for the species. Many of the elements of courtship in C. an~la are widespread in hummingbirds. Practice and probably learning play a major role in the maturation of song and dive displays in the individual. The courtship sequence in this hummingbird probably represents the resultant of various selective pressures, some acting mainly on males and others on females. Hummingbirds are becoming among the beststudied of North American birds, particularly with respect to energetic aspects of nesting (Horvath 1967, Calder 197 1, 1974, Calder and Booser 1973, Smith et al. 1974) territoriality and foraging (Stiles 197 la, Ewald and Carpenter 1978, Kodric-Brown and Brown 1979, Pyke 1978, Gass 1979) and relationships with the flowers they visit and pollinate (Stiles 1973, Carpenter 1978, Waser 1978, KodricBrown and Brown 1979, Price and Waser 1979). Recent field studies in California have disclosed a striking amount of hybridization among several (newly?) sympatric species (Lynch and Ames 1970, Wells et al. 1978, Wells and Baptista 1979). Study of hybrids and parental types in nature offers a unique opportunity to document the ecological and behavioral effects of such hybridization. Analyses of these phenomena, however, have been hindered by the lack of reliable descriptions of courtship and aggressive displays of the species concerned. The conspicuous dive displays have been described with varying degrees of completeness and accuracy by Bent (1940) Banks and Johnson (196 l), Wells et al, (1978) and Wells and Baptista (1979), among others, but except for the perceptive discussions of Pitelka (1942, 19 5 1 a, b) their role in courtship has been misunderstood. Moreover, a whole family of close-range displays in these hummingbirds, far more crucial in courtship per se, has been overlooked. Finally, I know of no good descriptions of display sequences nor, indeed, of copulation itself in these birds. Behavioral isolating mechanisms in North American hummingbirds cannot be properly appraised without a clear understanding of what actually constitutes their courtship. Through several years of close study of the ecology and behavior of the Anna’s Hummingbird (Calypte annu) and other California species (Stiles 1973) I was able to observe courtship and aggressive displays ofthese birds in detail. My purpose here is to describe and interpret the vocalizations and displays of the Anna’s Hummingbird, to serve as a basis for comparisons with other species.