Online advertising first became a serious business when Internet use increased in the late 1990s, but Web companies struggled to attract local merchants to use their services. Websites offered banner ads, for example, but that didn't work out for small businesses. Major tech companies bet on city-specific guides that never took off. Microsoft Corp. launched Sidewalk, which it sold in 1999, while AOL partnered with Citysearch. It wasn't until around 2008, when the daily-deals market came into play, that small businesses had an easily understood method of Web marketing. Groupon Inc. popularized the model in which Web companies sell vouchers for 50% or more off goods or services at local businesses, which pay no upfront costs. Get the full story at The Wall Street Journal