This paper analyses the increase in mothers' employment in Britain over 1974-2000 using the General Household Survey. We isolated those birth cohorts whose mothers experienced significant increases in employment and compared those increases to changes in policies. The results suggest that maternity rights have had a profound effect on employment, but this effect varies by the wage opportunities of mothers. Maternity rights have induced a behaviour change in when mothers return to work. Many who previously would not have gone back to work until their children were age 3-5 are now returning to work within the first year. This effect has been most marked among better educated and higher paid mothers.