Despite widespread concern about people experiencing homelessness, fundamental questions about this vulnerable and difficult-to-study population are unresolved. This dissertation draws on new data and innovative methods to fill critical gaps in our understanding of homelessness in the United States. The introduction discusses the general problem of homelessness, the state of existing literature, and the contributions and limitations of these essays. The first chapter examines the completeness and reliability of available data sources and develops a new estimate of the U.S. homeless population size. The second chapter examines the level and longitudinal patterns of income and safety net participation for people experiencing homelessness by linking the Census and other datasets to administrative tax and program data. The third chapter provides the first national calculation of mortality for this population, shedding new light on the health disparities associated with homelessness. Taken together, these essays provide researchers, policymakers, and the public with a the first national, close to representative, and rigorously quantitative description of the persistent hardships associated with homelessness while also informing future efforts to aid this population.