Animal space use is complex, from both the individual and population perspectives. Spatial memory leads to site fidelity, the emergence of home ranges, and multi-scaled use of the environment. Attraction to conspecifics--another memory-dependent property--contributes to population survival by counteracting decline in local abundance from unconstrained dispersal. However, memory effects, multi-scaled space use, and intra-specific cohesion present deep theoretical challenges for biophysical modelling. This book confronts these issues straight on, and presents a range of novel system descriptors, model designs, and simulations; intrinsic properties from memory and scaling are illustrated in detail, and classical models are scrutinized with respect to compliance with real data. The presentations of concepts are geared towards a broad audience of researchers and students with an interest in animal space use.The book advocates that an extension of the biophysical frame of reference may be needed to understand systems that express intrinsic complexity from the combined effects of scaling and memory. It boldly provides an overview and critical evaluation of existing concepts, and a wide range of theoretical proposals to resolve present challenges.