Time use studies analyze how individuals allocate their time. Data on time use allow researchers to document and understand human behavior and population lifestyles and to implement policies for development and planning policies (Harvey & Pentland, 1999). Time is a scarce resource that each person uses differently, and through the study of time we can analyze whether these differences are voluntary or forced and predict change in future population behavior (Duran, 2010). Time use data have been widely used to analyze changes over time and differences between cultures. For example, Bianchi et al (2006) used time use data for the United States from 1965 forward to analyze the time allocation patterns of changing American families. They found that decreases in housework and increases in multitasking help explain how mothers' time with children has remained steady despite increases in paid work. Gershuny (2000) found convergence in time use patterns both across time and across countries with different social and cultural backgrounds. In this chapter we introduce time use data as a resource for studying work and family. While we broadly introduce different types of time use data, our primary focus is on time diary data. We review the historical relevance of time use studies, and we describe data collecton methods. We discuss challenges for comparing time diary data across time and space. Finally, we include a case study illustrating how time diary data may be used to compare family time in the United States and Spain.