Yelp began as an email tool for asking friends for recommendations. Users liked writing reviews more, so reviews became the product. People rated restaurants, dentists, mechanics and more, and others read them before choosing where to go. Local businesses paid for ads and enhanced listings. When Yelp filed to go public in 2012, it had tens of millions of reviews, and smartphones made them easy to check on the spot. Its biggest rival was Google.

Two PayPal Alumni

Jeremy Stoppelman and Russel Simmons founded Yelp in 2004. Both had worked at PayPal. Their first idea was an email system for asking friends for recommendations. Users liked writing reviews more, and the founders followed them. The bet was that honest reviews from ordinary people would become the main guide for local decisions. The site started in San Francisco and spread city by city.

Fighting Google Over Search

Yelp priced at $15 a share in March 2012 and jumped on its first day. It kept growing as people searched for local businesses on their phones. Yelp fought with Google over search results and with businesses over its review filter. Its revenue came to rely on ads from local businesses and on services such as restaurant waitlists. Jeremy Stoppelman led it as chief executive, and Yelp remains public.

Cover: The Habit of Criticizing Others (Ta o soshiru kuse), from the series "Seven Bad Habits (Nakute nana kuse)", Kitagawa Utamaro. Art Institute of Chicago, public domain. Chosen for a habit of criticizing others (reviews).