Marijuana use has been decriminalized across the board in both Colorado and Washington, after voters passed ballot initiatives in the states on Tuesday -- a landmark victory for the legalization movement.

Image: Getty Amendment 64 in Colorado will amend the state constitution to legalize and regulate the production, possession, and distribution of marijuana for people age 21 and older. Washington State's I-502 does the same.

"Tonight, for the first time in history, two states have legalized and regulated the adult use and sale of cannabis," said NORML, a pro-legalization organization.

"The significance of these events cannot be understated."

"The voters have spoken and we have to respect their will," said Colorado Gov. John Hickenlooper, in a statement. "This is a complicated process, but we intend to follow through."

The governor went on to point out that cannabis is still illegal at the federal level. Experts predict this will eventually lead to a battle in the Supreme Court.

Across the country, there were six marijuana referendums in total. Three of them proposed legalization for recreational purposes; three proposed medical marijuana.

Massachusetts voters approved a referendum legalizing medical marijuana. Arkansas voters turned it down. Montana voters approved a referendum to place restrictions on its existing medical marijuana laws.

Oregon voters turned down their initiative to allow the commercial cultivation and sale of marijuana to adults.