The US Department of Housing and Urban Development (HUD) undertook an evaluation of its Lead Hazard Control Grant Program between 1994 and 1999. The Evaluation is the largest study ever done on the effectiveness of lead hazard controls implemented in residential dwellings. The Evaluation had several major objectives: determining the effectiveness of various lead hazard controls in reducing residential dust lead levels and children's blood lead levels, establishing the costs of doing lead hazard control work and factors that influence those costs, determining the rate of clearance testing failures and their causes, and identifying possible negative effects of lead hazard control work on children's blood lead levels. This paper reports the overall research design and data collection methods of the Evaluation. The large number of dwelling units enrolled in the Evaluation was possible only by the innovative partnership among HUD, the Evaluators, and the grantees. HUD and the Evaluators relied on the grantees for essentially all of the data collection. The 14 participating HUD Lead Hazard Control Grantees were responsible for implementing the lead hazard control programs in their communities and collecting the study data. This paper describes the methods for recruiting and enrolling dwellings and families, collecting environmental and housing data, interviewing participating families, and collecting data on lead hazard control work performed and its costs. The paper also describes the basic quality control and quality assurance procedures used. The principal outcome measures were lead in dust collected using wipes from floors, window sills, and window troughs and lead in blood collected from children who were 6 years old or younger at enrollment. Data collection was conducted before intervention, immediately postintervention, and 6 and 12 months postintervention. For a subset of dwellings undergoing an extended follow-up data were also collected at 24 and 36 months postintervention. This paper provides the context for subsequent reports that will describe such findings as the influence of lead hazard control work on serial dust lead levels, the influence of lead hazard control work on serial blood lead levels in children, the nature and costs of the lead hazard control work done at the dwellings, and the experience of the grantees in meeting clearance testing requirements.