The global loss of biodiversity has led to a renewed interest in the underlying mechanisms that explain spatial differences and temporal change of diversity. This book synthesises recent advances in our understanding of interactions that enhance or diminish coexistence among competing species. It features an innovative, spatial view of competition and coexistence. The chapters are logically grouped and stitched together by the central organising principle of spatial distribution and mobility of competing species and their resources. The text also covers ecological modelling and experimental evidence in the search for general principles across ecosystems, from lake plankton and rocky shore benthos to grasslands and insects.