Google has a dozen computer controlled cars - most of them Toyota Priuses -- equipped with self-driving technology.
Designers say the robotic vehicles could make roads safer, since most car accidents are the result of human error.
Governor Brown signed a bill that will set safety and performance regulations to test and operate the driverless cars on California roads.
GOV. BROWN: "Today we're looking at science fiction becoming tomorrow's reality, the self driving car"
Democratic Senator Alex Padilla authored the legislation that received bipartisan support.
PADILLA: "We can save lives, we can create jobs and ease congestion and reduce emissions in the process, that's a dream bill, whether you're an engineer or a politician."
In February, Nevada became the first state to approve regulations spelling out requirements for companies to test driverless cars.
Governor Signs Several Environment-Related Bills