Today marks the 15th anniversary of Apple's retail stores. Led by Steve Jobs, the Cupertino-based company opened its first two retail stores, one in Tysons Corner, Virginia and the other in Glendale, California, on May 19, 2001.

As Macworld recounts, Millard "Mickey" Drexler, who at the time served as president and CEO of fashion brand Gap, joined Apple's board of directors in 1999. A year later, Apple hired former Target marketing executive Ron Johnson who was responsible for transforming the retail store from a K-Mart clone into a trendy chain that specialized in affordable, well-designed housewares.

Johnson drew the assignment of developing Apple's retail plan. After what was described as a few false starts, he landed on the concept of focusing on the user experience of Apple's products.

During opening weekend, more than 7,700 people visited the two stores, purchasing a total of $599,000 worth of merchandise. That's an impressive haul when you consider the iPod hadn't even been released yet and the iPhone was still six years away.

Many critics believed the experiment would be a colossal failure but history has proven them wrong. These days, Apple's retail stores make more money per square foot than any other retail location. That's not surprising when you consider more than a million people step foot inside Apple Stores around the world every day.

Earlier today, in fact, Apple invited journalists to preview its new Union Square store in San Francisco. The store, which is powered by 100 percent renewable energy, will offer several new features and services including a massive 6K video wall, an outdoor plaza, private, hands-on advice and training to entrepreneurs and more.

The Union Square store opens to the public on May 21 at 10 a.m.

Last image courtesy Shara Tibken