Policy makers continue to debate Medicaid expansion under the Affordable Care Act, and concerns remain about low provider participation in the program. However, there has been little research on how various measures of physician participation may reflect different elements of capacity for care within the Medicaid program and how these distinct measures correlate with one another across states. Our objectives were to describe several alternative measures of provider participation in Medicaid using recently publicly available data, to compare state rankings across these different metrics, and to discuss potential advantages and disadvantages of each measure for research and policy purposes. Overall, we find that Medicaid participation as measured by raw percentages of physicians taking new Medicaid patients is only weakly correlated with population-based measures that account for both participation rates and the numbers of physicians per capita or physicians per Medicaid beneficiary. Participation rates for all physicians versus primary care physicians also offer different information about state-level provider capacity. Policy makers should consider multiple dimensions of provider access in assessing policy options in Medicaid, and further research is needed to evaluate the linkages between these provider-based measures and beneficiaries' perceptions of access to care in the program.