Tipping is a very American concept – most people around the world aren’t expected to tip because employers elsewhere are expected to actually pay a living wage to workers in the service industry.

Tipping culture has been expanding fast, too, and now it’s not just waiters, bartenders or hairdressers you’re expected to tip. More and more establishments where you wouldn’t normally tip are asking for something extra at checkout.

Dr. Melissa Dallas, professor emeritus, department of hospitality leadership at Missouri State University, answers some questions about tipping culture in the U.S. on WalletHub.