The marijuana measure in Washington sets up a showdown with a federal government, which outlaws the drug's prohibition. The measure establishes a system of state-licensed marijuana growers, processors and retail stores, where adults over 21 can buy up to an ounce. It also establishes a standard blood test limit for driving under the influence.
Estimates have showed pot taxes could bring in hundreds of millions of dollars a year, but the sales won't start until state officials make rules to govern the legal weed industry.
The outcomes of similar measures in Colorado and Oregon were uncertain.
In Massachusetts, voters approved a measure to allow marijuana use for medical reasons, joining 17 other states. Arkansas voters were deciding on a similar measure that would make it the first Southern state in that group.