Identifying and characterizing the factors that modulate longevity is central to understanding the basic mechanisms of aging. Among model organisms used for research related to aging, the budding yeast has proven to be an important system for defining pathways that influence life span. Replicative life span is defined by the number of daughter cells a mother cell can produce before senescing. Over the past 10 years, we have performed replicative life span analysis on several thousand yeast strains, identifying several hundred genes that influence replicative longevity. In this chapter we describe our method for determining replicative life span. Individual cells are grown on solid media and monitored from their initial undivided state until they undergo senescence. Daughter cells are manually removed using a fiber optic needle and quantified to determine the total number of times each mother cell divides.