The evolutionary ecology and population sytematics of the genus Phelsuma (Gekkonidae) were studied in the Seychelles. The distributions of all 18 Seychelles lizard species are described. These give little evidence for species turnover or the equilibrium model of island biogeography. Aspects of Phelsuma behaviour, social systems and reproduction were investigated. Phelsuma can digest pollen, which, with nectar may constitute a large part of the diet. On Praslin, P.sundbergi and P.astriata breed throughout the year, and partition their macro-habitat, micro-habitat and food resource dimensions such that P.sundbergi mainly occupies nectiferous and polliniferous palms and larger hardwood trees, whilst the smaller P.astriata is found on non-flowering palms and smaller trees. Interspecific competition is demonstrated by population density and habitat shifts between populations on islands in sympatry and allopatry. The biomass of Phelsuma geckos supported by coconut plantations in sympatric and allopatric situations tends to be relatively constant, such that there are either more small geckos or fewer large geckos. It is suggested that large body size is an adaptation to the defence of predictable and defensible food sources, such as palm flowers. Racial differention was investigated by multivariate morphometrics of shape, scalation and colouration, using appropriate techniques to negate ontogenetic effects. In the granitic islands, three phenetic aggregations of island populations were identified in the P.madagascariensis group, and two aggregations in the P.astriata group. Conventional taxonomic methods have failed to illustrate these patterns of phenetic variation, and new classification of island populations is proposed. Primary patterns of racial differentiation appear to have arisen from the sectioning of pre-existing clinal variation by rising Holocene sea levels, while secondary patterns relate to recent ecological selection pressures. P.abbotti populations on Aldabra and Assumption are sub-specifically distinct and not conspecific with granitic island forms. P.laticauda on the Farquhar group are probably not subspecifically distinct from Madagascan populations. All other coralline island populations appear to be recent introductions from the granitic islands.