Signed into law on April 19, 2004, Senate Bill (S.B.) 899, Stats. 2004, ch. 34 created the groundwork for Medical Provider Networks (MPNs) as an instrument to address concerns with upward spiraling medical costs and limitations on access to care. In 2013, major changes to the MPN system were implemented through passage of Senate Bill (S.B.) 863, Stats. 2012, ch. 363. This document discusses the statutory and regulatory provisions governing MPNs. For information on the other provisions of S.B. 899 and S.B. 863, see CMA ON-CALL document #7300, “Basics of the Workers’ Compensation System”; CMA ON-CALL document #7303, “Medical-Legal: Evaluations, Reports, and Payment”; CMA ON-CALL document #7305, “Qualified Medical Evaluators (QMEs): Requirements and Responsibilities”; CMA ON-CALL document #7308, “Treating Physicians: Obligations and Reports”; CMA ON-CALL document #7309, “Treating Physicians: Payment For Treatment (OMFS)”; and CMA ON-CALL document #7310, “Utilization Review.”