This User Guide provides information on the Panel Study of Income Dynamics (PSID). The 2003 PSID is a nationally representative sample of over 7,000 families. The PSID began in 1968 with a sample of 4,800 families and re-interviewed these families on an annual basis from 1968-1997. Since then, it has re-interviewed them biennially. Following the same families and individuals since 1968, the PSID collects data on economic, health, and social behavior. (See http://psidonline.isr.umich.edu/ for detailed information on the PSID). Initially, the PSID identified disability by asking the head of the household whether he, or she when no adult male is present, had a physical or nervous condition that limits his or her ability to work. In 1981 the PSID began asking the head this question with respect to his spouse. Additional questions that provide an opportunity to expand this definition of disability were included in 2003. The User Guide makes use of these new questions to estimate the size of the population with disabilities and the prevalence rate of disability in the population, as well as the employment rate and level of economic well-being. The major strength of the PSID for those interested in disability research is its long-running information on families. No other nationally representative survey has captured such detailed information on the same families over such a long time. Such longitudinal data allows researchers to better understand the dynamics of the disability process and its consequences. Here we demonstrate the comparative advantage of the PSID over traditional cross-sectional data sets. Using the PSID, we identify persons with disabilities of various lengths and show the sensitivity of alternative definitions of the population with disabilities based on the duration of a disability. We also measure how the employment and economic well-being of individuals changes following the onset of a disability. Finally, we provide examples of how the PSID has been used with the German Socio-Economic Panel (GSOEP) to compare the employment and economic well-being of working-age people with disabilities in the United States and Germany. This analysis uses the equivalized data from these longitudinal datasets contained in the Cornell University Cross-National Equivalent File (CNEF).