Lizards utilise many different niches across a large variety of habitats. As a result of selective pressures exerted by the particular environments, many lizards in similar habitats have been shown to exhibit convergent morphologies. The performance of a lizard, or any organism for that matter, is a fundamental attribute employed in its survival, and therefore significantly impacts its fitness. The study of an organism’s functional capacity is fairly new, with relatively few studies published. In studies of lizard functional capacity, performance is most often defined as the whole organism’s ability to conduct an ecologically relevant task, and measures thereof have included sprint speed, bite force and locomotor endurance, amongst others. Primarily, the study of whole-organism performance includes those performance aspects related to dynamic animal movements, and not more passive’ performance aspects (such as immune function levels or reproductive output) or those performance traits measured within an organism (such as enzyme reaction rate). This book focuses on the thermal ecology, genetic diversity and functional role lizards have in ecosystems. It discusses the influence of light on visual discrimination of sexually dichromatic dewlap colour in male and female brown anoles; the tolerance to thermal stress in lizard embryos; the leiolepis guttata; the impact on habitat modifications of thermoregulation in coastal sand dunes; the convergence in morphology in lizards; and sexual dimorphism and thermoregulatory behaviour in the long-tailed spiny lizard.