Measuring the characteristics of managed care plans and of the health care markets in which the plans operate is a complex undertaking. Based on a previously developed framework of health plan factors, we review measures of managed care plans and the characteristics of the area in which an individual resides using two national surveys, the Medical Expenditure Panel Survey (MEPS) and the National Health Interview Survey (NHIS), and other data sources such as the Area Resources File and the United States census. We provide empirical applications of these measures and also discuss common analytical issues that should be considered. Despite the many analytical challenges presented by these complex surveys, the MEPS and NHIS are rich sources of data for examining the impact of health plans and the characteristics of markets or areas on health care expenditures and outcomes.