During the decades of the 1870s and 1880s, urban mortality, fertility and nuptiality patterns all appear to have almost simultaneously begun to enter a new era. The demographic history of urban Britain during the period 1840-1950 is particularly dominated by the dramatic changes in mortality and fertility occurring during the central decades of that period. However, attempts to verify empirically a direct relationship between mortality and fertility change in this period in Britain including careful efforts to distinguish infant from child and other forms of mortality, have only resulted in negative or contradictory statistical findings. This chapter offers separate treatments of the history of changing urban mortality and fertility, reflecting the two distinct bodies of historiography. Two principal features dominate urban mortality patterns in the period 1840 to 1950, initially high death rates, and a gradual shift in the main causes of death from infectious to chronic and degenerative diseases.