"From ecosystems to Facebook and from the internet to the global financial market, networks play a central role in nature and society. Phenomena such as climate change, pandemics, and financial crises are based on networked structures; and networks give insights into how social environments effect health and behaviour. In this Very Short Introduction, Guido Caldarelli and Michele Catanzaro discuss the nature and variety of networks, using familiar examples from society, technology, nature, and history. They show how networks self-organize and the role they play in processes like large-scale blackouts and computer virus outbreaks. They also describe the wide and important applications of network theory in a range of areas, including genetics, ecology, technology, and management."--Publisher description.