There was a time when consumer goods companies paid musicians, athletes, and actors for endorsements, or to license their name and likeness. But in recent years, there's been an explosion of celebrities getting into business directly, selling everything from shapewear to tequila. Ayelet Israeli, professor at Harvard Business School, says the growth of social media and online, direct-to-consumer retail accelerated this trend, but notes that not all celebrity brands are a success. She explains what works and doesn't, and outlines lessons for non-famous entrepreneurs and established companies. Israeli is coauthor of the HBR article "What Makes a Successful Celebrity Brand?"