Recent focus on global climate change has elevated interest in understanding natural populations evolutionary adaptation to temperature and predicting how these populations may respond to temperature changes. This book addresses three aspects of adaptation to temperature focusing on Daphnia (Crustacea: Cladocera) as a model system. First, it discusses and examines the validity of the controversial assumption that can also be described by a proverb “jack-of-alltrades is a master of none". Second, it examines genetic variation and heritability of thermal tolerance of three Daphnia populations and provides predictions how these populations would adapt to a changing thermal environment. Third, it examines the effect of optimal/stressful temperatures on Daphnia juvenile survivorship and how such effects could influence the evolution of reproduction. This book should help shed some light on this important and active field and, should be of considerable interest to researchers in thermal, adaptation and evolutionary biology, graduate and advanced undergraduate students as well as professionals interested in adaptation to temperature.