Objective. To describe the growth of any willing provider (AWP) and freedom of choice (FOC) laws applicable to managed care firms and to explore empirically the determinants of their enactment. Study Setting. A 1996 compendium of state laws and state-level data from the 1991-1994 period. Study Design. Pooled cross-section time-series logistic regression of the decision to enact various types of AWP and FOC laws. Analysis uses a public choice framework to examine enactment. Key variables include proxy measures of proponent and opponent strength and the political environment. Principal Findings. The model works well for laws affecting hospitals, but performs poorly for physician and pharmacy laws. More providers are associated with the enactment of AWP and FOC laws. More large employers are associated with a reduced likelihood of enactment of some forms of the laws but not others. Conservative states are more likely to enact laws limiting selective contracting with hospitals and physicians. States with greater interparty competition are also more likely to adopt some types of legislation. Conclusions. The empirical results generally are consistent with the view that AWP and FOC laws are often enacted as a defensive strategy on the part of providers, but additional research is needed to provide a more definitive assessment of the determinants of these laws. Suggestions for future research are provided.