Approximately one third of dairy cows are replaced every year. Replacement of dairy cattle is an important part of the cost of dairy production and an environmental sustainability concern. Primary culling reasons are reduced health and fertility. Reduced welfare often proceeds culling. This chapter focuses on factors that affect replacement and culling in dairy herds with a focus on cows. The act of culling is simple, but the risk factors and economic considerations are complex. The chapter first presents some data on culling risks and reasons, explores more in depth the effects of poor health on culling, and presents aspects of economic decision making regarding culling and replacement decisions.