In this series of articles on the Mental Capacity Act 2005 (MCA) the author now turns to the interrelation between mental capacity and mental disorder and between the Mental Health Act 1983 (MHA) (as amended by the Mental Health Act 2007 [MHA, 2007]) and the Bournewood safeguards. The article explains how the MCA and the MHA are designed to cover distinct situations: the one mental capacity; the other mental disorder and the different definitions are considered. The article also looks at the different principles which apply and the different powers available under each Act. The different forms of protection under each Act are contrasted. Because of criticism of the UK by the European Court of Human Rights in the Bournewood case, amendments have been made by the MHA 2007 to the MCA to provide protection for those incapable of making decisions who suffer from mental disorder and whose best interests require a loss of liberty.