Within months of going public, Mediaplex was worth billions on a simple promise: software could decide which ad each person saw. Early web ads were mostly banners bought by hand and measured loosely. The San Francisco company offered real machinery to pick the ad, the moment and the viewer, then measure the result. When it filed in late 1999, internet ad spending was rising fast, and marketers wanted proof the money worked.

Agency Meets Ad Server

Gregory Raifman founded Mediaplex in San Francisco in 1996. He bet that online advertising would come to run on data and software, with messages that changed based on the viewer and the moment. Mediaplex paired the services of an agency with its own ad-serving technology, called MOJO. Clients could use it to run complex campaigns across many sites at once.

Folded Into ValueClick

Mediaplex priced at $12 a share in November 1999. Then the online ad market collapsed in 2000 and 2001, and many of its dot-com clients disappeared with it. In 2001 ValueClick bought Mediaplex in a stock deal, two years after the offering. Raifman stayed on the ValueClick board into 2002. The Mediaplex ad-serving technology lived on inside ValueClick for years after the merger.

Cover: Street Advertising, John Thomson. Art Institute of Chicago, public domain. Chosen for street advertising posters (the ad, placed where people look).