quality:correction, structural:summarization
Adler & Sullivan (1888–1893)

Wright learned that the Chicago firm of Adler & Sullivan was "... looking for someone to make the finished drawings for the interior of the Auditorium Building ". Wright demonstrated that he was a competent impressionist of Louis Sullivan's ornamental designs and two short interviews later, was an official apprentice in the firm. Wright did not get along well with Sullivan's other draftsmen; he wrote that several violent altercations occurred between them during the first years of his apprenticeship. For that matter, Sullivan showed very little respect for his own employees as well. In spite of this, "Sullivan took under his wing and gave him great design responsibility." As an act of respect, Wright would later refer to Sullivan as lieber Meister (German for "dear master"). He also formed a bond with office foreman Paul Mueller. Wright later engaged Mueller in the construction of several of his public and commercial buildings between 1903 and 1923.

By 1890, Wright had an office next to Sullivan's that he shared with friend and draftsman George Elmslie, who had been hired by Sullivan at Wright's request. Wright had risen to head draftsman and handled all residential design work in the office. As a general rule, the firm of Adler & Sullivan did not design or build houses, but would oblige when asked by the clients of their important commercial projects. Wright was occupied by the firm's major commissions during office hours, so house designs were relegated to evening and weekend overtime hours at his home studio. He later claimed total responsibility for the design of these houses, but a careful inspection of their architectural style (and accounts from historian Robert Twombly) suggests that Sullivan dictated the overall form and motifs of the residential works; Wright's design duties were often reduced to detailing the projects from Sullivan's sketches. During this time, Wright was assigned to work on the Sullivan's bungalow (1890) and the James A. Charnley bungalow (1890) in Ocean Springs, Mississippi, the Berry-MacHarg House, James A. Charnley House (both 1891), and the Albert Sullivan House (1892), all in Chicago.

Despite Sullivan's loan and overtime salary, Wright was constantly short on funds. Wright admitted that his poor finances were likely due to his expensive tastes in wardrobe and vehicles, and the extra luxuries he designed into his house. To supplement his income and repay his debts, Wright accepted independent commissions for at least nine houses. These "bootlegged" houses, as he later called them, were conservatively designed in variations of the fashionable Queen Anne and Colonial Revival styles. Nevertheless, unlike the prevailing architecture of the period, each house emphasized simple geometric massing and contained features such as bands of horizontal windows, occasional cantilevers, and open floor plans, which would become hallmarks of his later work. Eight of these early houses remain today, including the Thomas Gale, Robert Parker, George Blossom, and Walter Gale houses.

As with the residential projects for Adler & Sullivan, he designed his bootleg houses on his own time. Sullivan knew nothing of the independent works until 1893, when he recognized that one of the houses was unmistakably a Frank Lloyd Wright design. This particular house, built for Allison Harlan, was only blocks away from Sullivan's townhouse in the Chicago community of Kenwood. Aside from the location, the geometric purity of the composition and balcony tracery in the same style as the Charnley House likely gave away Wright's involvement. Since Wright's five-year contract forbade any outside work, the incident led to his departure from Sullivan's firm. Several stories recount the break in the relationship between Sullivan and Wright; even Wright later told two different versions of the occurrence. In An Autobiography, Wright claimed that he was unaware that his side ventures were a breach of his contract. When Sullivan learned of them, he was angered and offended; he prohibited any further outside commissions and refused to issue Wright the deed to his Oak Park house until after he completed his five years. Wright could not bear the new hostility from his master and thought that the situation was unjust. He "... threw down pencil and walked out of the Adler & Sullivan office never to return". Dankmar Adler, who was more sympathetic to Wright's actions, later sent him the deed. However, Wright told his Taliesin apprentices (as recorded by Edgar Tafel) that Sullivan fired him on the spot upon learning of the Harlan House. Tafel also recounted that Wright had Cecil Corwin sign several of the bootleg jobs, indicating that Wright was aware of their forbidden nature. Regardless of the correct series of events, Wright and Sullivan did not meet or speak for 12 years.