DoubleClick counted every banner ad it showed and every click it got, a kind of proof print and television could never give advertisers. By early 1998 banner ads paid the bills for much of the web, but placing them was crude. DoubleClick ran the servers that delivered ads to thousands of sites. It used data about each visit to pick the ad, targeting people by interest, location, or time of day. The New York company went public in February 1998.

Advertising You Could Measure

Kevin O'Connor and Dwight Merriman founded DoubleClick in 1996. The bet was that technology could make web advertising measurable in a way print and television never were. DoubleClick sold ads across a network of sites. It also licensed its ad-serving tools to large publishers. Its system counted every impression and every click. By its offering, DoubleClick was the leading name in online advertising.

A Privacy Uproar, Then Google

DoubleClick priced its offering at $17 a share in February 1998, and the stock rose dramatically through 1999. In 2000 its plan to merge web data with offline customer records set off a privacy uproar. Hellman & Friedman took the company private in 2005. Google acquired DoubleClick in 2008 for about $3.1 billion. DoubleClick's ad tools became a core part of Google's advertising business.

Cover: The Twin Brothers Ludwig and Emil Schulthess, Hans Jakob Oeri. Art Institute of Chicago, public domain. Chosen for twin brothers (double).