This book seeks to explain how and why complexity in the modern welfare system has grown; to identify the different ways in which legal and associated administrative arrangements are classifiable as 'complex'; to discuss the effects of complexity on the system's administration and its wider implications for rights and the citizen-state relationship; and to consider the role that law can play in the simplification of schemes of welfare. While primarily focused on the UK welfare system it also provides analysis of relevant policies and experience in various other states.