This edited volume on the nematode model Pristionchus pacificus describes an integrative approach to evolutionary biology. It aims for a merger of evolutionary and comparative biology with mechanistic approaches based on genetics and molecular biology. Insight into the function of biological systems obtained from laboratory studies when complemented with ecology, natural variation and natural history of an organism, can provide detailed knowledge of the proximate and ultimate causations of species. Ralf J. Sommer developed P. pacificus as model system for integrative evolutionary biology with case studies in evo-devo and population genetics on La Reunion Island. Similarly, ecological interactions with scarab beetles revealed examples for the evolution of novelty at the morphological and behavioural level and their underlying molecular mechanisms. Contributors include Paul W. Sternberg, Ralf J. Sommer, Jagan Srinivasan, Christian Roedelsperger, Frank C. Schroeder, Robin M. Giblin-Davis, Natsumi Kanzaki, Matthias Herrmann, Angela McGaughran, Katy Morgan, Akira Ogawa, Federico D. Brown, Ray E. Hong, Robbie Rae, Amit Sinha, David Rudel, and Erik J. Ragsdale.