While there is no universally agreed definition of a chimera, it is generally accepted that such states occur in networks of coupled oscillators where some fraction of the oscillators synchronise while the remainder are asynchronous. Since their discovery in 2002 and naming in 2004 there have been many papers on this topic, and several reviews published. This is one of them and it is comprehensive, with over 300 references. The main sections cover the different types of oscillators used in networks supporting chimeras (Sec.~2), the mathematics of chimeras (the Ott/Antonsen ansatz and various measures to characterise chimeras, Sec.~3), different types of chimeras (multi-headed, breathing, travelling, Sec.~4), different types of networks in which chimeras have been observed (2 and 3D lattices, multilayer networks, Sec.~5) and control of chimeras (Sec.~6). This review is uncritical, with conjectures and analogies presented as undisputed facts. It contains misunderstandings by the authors (``it is believed that the neurons are in the chimera state for visual orientation tuning and the head direction system in rats'') and they have reproduced poor choices of notation by others (e.g.~writing \(g(|D|=0)\) when \(g(D)\) is a probability density function). The quality of English is poor in places (``the chimera state in neuronal networks should be depicted in the microscopic view to be able to make a fantastic process on the exploration of chimera related diseases'').