Book excerpt: This book offers an overview of the larva of Diptera Cyclorrhapha. It first discusses the principal forms, functions and roles of larvae, and then evaluates feeding, locomotion and respiration in larval saprophages, phytophages and zoophages as keys to understanding and predicting larval morphology. It also highlights how the environment affects morphology, the adaptiveness of morphological features and compares the adaptive features. Assessing the larval attributes that have the potential to explain the success of the Cyclorrhapha, the book also suggests future research directions and provides a summary of main findings and conclusions. As such, it appeals to entomologists, evolutionary biologists and Diptera researchers in all fields.