For most of the twenty years since California passed Proposition 215, the medical cannabis industry in California existed in a regulatory gray area. Illegal under federal law, and treated as an affirmative defense under California law, the modest regulatory guidance provided by the State consisted solely of SB 420, which codified existing judge-made law regarding collective cultivation and distribution, and the Attorney General Guidelines of 2008, which gave further guidance to patients, collectives and law enforcement. No longer. In 2015 the legislature took the plunge in an attempt to regulatory guidance and economic certainty to an explosive growth market. Three bills collectively became known as the Medical Marijuana Regulation and Safety Act (subsequently renamed Medical Cannabis Regulation and Safety Act, but colloquially still referred to as MMRSA). The Act provides for seed to sale tracking, quality testing, water quality regulation, and formalized distribution based on the alcohol model. More significantly for practitioners, MMRSA (called “mersa”) enshrined local control into law, leading to a patchwork of radically divergent regulations in different cities and counties across the state. Since a local permit is a perquisite for obtaining a state-wide license when the Bureau of Medical Cannabis Regulation begins to issue state-wide licenses on January 1, 2018, practitioners need to be well-versed in local land use and planning ordinances. For example, large swaths of the state have issued outright bans to give local governments time to decide how they want to regulate medicinal cannabis, if at all. On the other hand, Humboldt County fully embraced MMRSA, and has enacted county regulations that hew closely to MMRSA itself. At the other end of the spectrum, short of an outright ban, is the city of West Sacramento, which, well-located close to several major freeways, is positioning itself as a distribution hub, but is not allowing cultivation or retail sales (go here: http://qcode.us/codes/westsacramento/; then search for “Chapter 17.42 Additional Permitted Uses” and go to “CodeAlert Amendment Page” to find ordinance, then click on left column). It chose to issue a single medicinal cannabis permit for one distribution facility, with extensive security required by ordinance. Oakland is maneuvering itself into position as a cannabis capital of the state, and is well-along in its endeavor to offer local permits that mirror the requirements of the state-wide license scheme, although Oakland did institute an equity program that requires fifty-percent of all licensees to be issued to residents from certain disadvantaged parts of town. San Francisco has one of the most permissive schemes in the state, with no limit on the number of permitted dispensaries, which are restricted solely by proximity to schools and youth facilities. Some cities, like Los Angeles, offer limited criminal immunity to its dispensaries, which has not been interpreted to be equivalent to an actual local license described in MMRSA; these cities must either issue dispensing permits/licenses or MMRSA has to be amended to recognize these allowances. Finally, the Gold Country, long a hotbed for cannabis cultivation, has chosen radically different paths from county to county. El Dorado County is moving methodically towards regulation, whereas Nevada County chose to allow and regulate indoor cultivation, but enacted an outright ban on outdoor cultivation, citing environmental, nuisance, and other considerations and, after reconsidering its position in July 2016, failed to repeal the ban. With fifty-eight counties, four hundred and eighty-two municipalities, and recreational use potentially on the horizon, California cannabis practice promises an unstable regulatory landscape for practitioners for years to come, even if Proposition 64 is passed in November. Practitioners in the field need to stay consistently abreast of local developments, as the laws and regulatory schemes shift under our feet. Burke Hansen is a San Francisco medical cannabis, land use and trusts attorney with Hallinan & Hallinan P.C., and the CEO of Coalition for Common Sense Regulation Inc., a California not-for-profit corporation devoted to helping local communities develop functional and localized medical cannabis regulation. .