He did not form any close friendships, even though Sullivan himself took a liking to him. Sullivan engaged him in a five-year contract. The contract would later become a subject of contention, for it stated that Wright could not participate in outside work. When Sullivan discovered that Wright was taking on extra commissions, he ordered him to stop. The relationship came to an end. Wright left Sullivan and began to work on his own. He founded his own practice at just 25 years of age and with design after design he never looked back. His Unitarian faith -- and the philosophy he had learned from Sullivan -- helped inform each of his designs. With some new associates, Wright formed the Prairie School -- a distinctly American style of architecture. Wright himself worked on the Winslow House, which emphasized line and horizontal elements and all of Wright's designs emphasized the use of natural materials and were usually not painted. The rooflines of his designs utilized low pitched rooflines with deep overhangs and long lines of uninterrupted windows so that the structure merged into the surrounding environment. Most of the homes that he designed had a large stone or brick fireplace that was used to unify the house and each room in the house was open to all...

In a single year (1900-1901), he designed and erected four different houses, all exciting examples of the Prairie Style that united building with landscape through theme, line, and structure. By his 40th year, Wright was a much admired architect recognized as being on the cutting edge of innovation and style.
One of Wright's most famous works is "Robie House." Wright designed this house at age 42. In Robie House (1909) -- Wright's best example of the American architectural style -- the Prairie Style -- Wright laid bare the essence of American Unitarianism. What the Prairie Style lacked in ornament, it made up for in horizontality. This type of architecture was an expression of his spirituality and philosophy: form was following function. It attempts to resemble the Midwestern landscape surrounding it.

By his 40s, Wright had fallen in love with another woman, the wife of a client. With this woman, Mamah Borthwick Cheney, Wright, however, fled to Europe leaving both his and her children behind. The two spent nearly two years in Europe, living in Italy, where Wright continued to do his work.

The two returned to America