The article considers the new options since the millennium for same sex and opposite sex couples to formalise their relationships. The history of the changing attitudes to same sex relations is traced and their progressive recognition in the legislation of same sex civil partnership and marriage. The somewhat puzzling sequence of the legislation of civil partnerships, and same sex marriage is explored, and can be understood in terms of the initial opposition to same sex civil partnerships (and insistence of their non-equivalence to marriage), and then increasing pressure for greater choice and equal status. Trends in the numbers of civil partnerships and same sex marriages are analysed and evaluated, and some rough estimates made of the dissolution rates of same sex couple civil partnerships and divorce rates of same sex couple marriages. Currently civil partnership and marriage is available for both same sex and opposite sex couples - symmetry has been achieved. But there is no symmetry, nor equality, in the option of converting one form of legal union into another; only one is possible. The Government undertook a consultation exercise on conversions but has not published the findings, or its response. The article explores the options and considerations for this next stage of development.