"Accompanying the rapid rise of unmarried cohabitation and the decline in nuptiality, Britain experienced a sharp increase in the number and proportion of births outside wedlock....84% of this recent increase corresponds to jointly registered births which can therefore be assumed to occur to informal couples. This chapter explores this new fertility trend using General Household Survey data for 1989, focusing on first births to single never-married cohabitants. The informality of cohabitation as a living arrangement and shortfalls in the data...are discussed....The chapter then attempts to provide some insights into the circumstances of the first birth, the timing of birth and marriage and the relative levels of fertility in the different unions."