In November 2004, voters in the U.S. state of California passed Proposition 63, the Mental Health Services Act (MHSA), which has been designed to expand and transform California's county mental health service systems. The MHSA is funded by imposing an additional one percent tax on individual, but not corporate, taxable income in excess of one million dollars. In becoming law in January 2005, the MHSA represents the latest in a Californian legislative movement, begun in the 1990s, to provide better coordinated and more comprehensive care to those with serious mental illness, particularly in underserved populations. Its claim of successes thus far, such as with the development of innovative and integrated Full Service Partnerships (FSPs), are not without detractors who highlight many problems but especially a lack of oversight, large amount of unspent funds, poor transparency, lack of engagement in some communities, and a lack of adherence to required reporting as challenges MHSA implementation must overcome to fulfill the law's widely touted potential.