OLYMPIA, Wash. - Gov. Chris Gregoire has signed into law a measure that legalizes same-sex marriage in Washington state, which now joins several other states that allow gay and lesbian couples to wed.

Gregoire and Secretary of State Sam Reed certified the election Wednesday afternoon, as they were joined by couples who plan to wed. The law does not take effect until Thursday, when couples can start picking up their wedding certificates and licenses at county auditors' offices. King County, the state's largest and home to Seattle, and Thurston County, home to the state capital of Olympia, were opening the earliest, at 12:01 a.m. Thursday, to issue marriage licenses.

Because the state has a three-day waiting period, the earliest that weddings can take place is Sunday. Couples who previously wed in another state that allows gay marriage, such as Massachusetts, will not have to get remarried in Washington. Their marriages will be valid here as soon as the law takes effect.

"This is a very important and historic day in the great state of Washington," Gregoire said before signing the measure that certified the election results. "For many years now we've said one more step, one more step."

Last month, Washington, Maine, and Maryland became the first states to pass same-sex marriage by popular vote. They joined six other states - New York, Connecticut, Iowa, Massachusetts, New Hampshire, Vermont - and the District of Columbia that had already enacted laws or issued court rulings permitting same-sex marriage.

Maryland's law officially takes effect Jan. 1, however couples can start picking up marriage licenses Thursday. Maine's law takes effect Dec. 29.