Abstract We studied the consequences of monogamy and polygyny for male and female lapwings at a site in northern England between 1993 and 1995. Males and females differed in breeding behaviour, and thus the pattern of reproductive investment: males contributed less time than females to the care of their offspring and more time to mating behaviour. We argue that this has resulted from sexual selection. Reproductive behaviour was similar in monogamous and polygynous individuals of both sexes. Male mating success was related to territory size, with males on the largest territories gaining more females. Polygynous male lapwings reared on average between 58 and 100% more chicks each year than monogamous males because of fewer complete breeding failures; between-year return rates of males to the area were similar. This would result in a strong advantage in terms of lifetime reproductive success for polygynous male lapwings. The seasonal breeding success of polygynous females was marginally, but not significantly, lower than that of monogamous females. Between-year return rates of monogamous and polygynous females were similar.