Here's what sets the city apart from states that have legalized:
HOW DID THIS HAPPEN?
Nearly two-thirds of District voters approved a November ballot initiative legalizing pot for recreational purposes. Congress tried to block it by inserting language in a subsequent spending bill, but District leaders said the initiative had already become law and couldn't be undone by Congress pulling funding. The initiative took effect Thursday.
WHAT'S LEGAL AND WHAT'S NOT?
People 21 and older can possess and use up to 2 ounces of pot or grow up to three mature plants in private homes. People can also give as much as 1 ounce away to another person.
WHAT'S PRIVATE, WHAT'S PUBLIC?
The city sums it up in four words: "home grow, home use." Smoking in public or in cars, restaurants, bars and coffee shops remains illegal, and the city is moving to ban it in private clubs. Possession also is illegal in public housing, but Police Chief Cathy Lanier said local police won't make arrests there for possession. Federal officers can make such arrests, however.
WILL POT BE AVAILABLE FOR SALE?
No. Congress explicitly banned the District from establishing laws allowing for marijuana to be sold, taxed or regulated, as Colorado and Washington state have done.
WASN'T POT ALREADY LEGAL?
The District has allowed medical marijuana and decriminalized possession of small amounts of pot last year, replacing arrests with $25 civil fines. Now the fines are gone, too.
WHAT'S THE ROLE OF CONGRESS?
The District has had "home rule" power to make its own laws for 40 years, but Congress still has the final word. Federal lawmakers commonly forbid policies they oppose by attaching language to crucial legislation, like the federal spending bill President Barack Obama signed in December.
ARE CITY LEADERS IN TROUBLE NOW?
House Judiciary Chairman Jason Chaffetz, a Utah Republican, warned Mayor Muriel Bowser that she and other city officials could face prison under a law banning federal agencies from spending unappropriated money. But Congress can't prosecute anyone, and the Justice Department is highly unlikely to do so. Congress can still sue, or pull funding for other city programs.
CAN YOU SMOKE A JOINT ON THE NATIONAL MALL?
No. Even possessing pot on federal property remains illegal, just as it is in Colorado and Washington state, which have huge swaths of U.S. land. Complicating matters, the District has 59 inner-city squares and triangles in federal jurisdiction. Since decriminalization took effect last year, 30 people have been arrested for possession on federal property, Lanier said.