Proposition 65 requires businesses to provide warnings to Californians about significant exposures to chemicals that cause cancer, birth defects or other reproductive harm. These chemicals can be in the products that Californians purchase, in their homes or workplaces, or that are released into the environment. By requiring that this information be provided, Proposition 65 enables Californians to make informed decisions about their exposures to these chemicals.

Proposition 65 also prohibits California businesses from knowingly discharging significant amounts of listed chemicals into sources of drinking water.

Proposition 65 requires California to publish a list of chemicals known to cause cancer, birth defects or other reproductive harm. This list, which must be updated at least once a year, has grown to include approximately 900 chemicals since it was first published in 1987.

Proposition 65 became law in November 1986, when California voters approved it by a 63-37 percent margin.  The official name of Proposition 65 is the Safe Drinking Water and Toxic Enforcement Act of 1986.