Approximately half of the total UK population is in receipt of one or more welfare benefits, giving rise to the largest single area of government expenditure. The law and structures of social security are highly complex, made more so by constant adjustments as the government pursues its often conflicting economic, political, and social policy objectives. This complexity is highly problematic. It contributes to errors in decision making and to increased administrative costs, and is seen as disempowering for citizens, thereby weakening enjoyment of a key social right. Current and previous UK administrations have had a commitment to simplify the benefits system. It is a specific objective underlying the introduction via the Welfare Reform Act 2012 of Universal Credit in place of diverse benefits, although it is not clear that the reformed system will be legally less complex and better for citizens to access. The book explains how and why complexity in modern welfare systems has grown. It identifies the different ways in which legal and associated administrative arrangements are classifiable as 'complex,' and it discusses the effects of complexity on the system's administration and its wider implications for rights and the citizen/state relationship. The book also considers the role that the law can play in the simplification of schemes of welfare. It makes reference not only to the UK welfare system, but also relevant policies and experiences in various other States. Law in a Complex State is an interesting and topical study for all those interested in welfare law.