Beginning Saturday, e-cigarette use will be barred from farmers' markets, parks, recreational areas, beaches, indoor workplaces, outdoor dining areas and other places where tobacco smoking is restricted.
"Vaping," however, will still be allowed in vaping lounges and stores and during theatrical performances.
The Los Angeles City Council unanimously passed the ban in March, citing potentially dangerous health effects. Los Angeles County health officials insist the vapor is dangerous.
Some e-cigarette users say vaping has actually helped them quit tobacco smoking.
Cindy Club, a lounge in Koreatown, planned a party to mark the changing law.
Richard Park, the club's manager, said it is not a "well-known fact (vaping) is going to be banned." Patrons after today "will be surprised when I'm going to have to ask them to go outside to vape," he said.
E-cigarettes were introduced in 2007, and were largely unregulated because they don't burn tobacco. They vaporize liquid instead. It looks like smoke, but people are exhaling vapor that's typically infused with nicotine.
City News Service contributed to this report.