The major event in the recent history of the American Thoracic Society (ATS) is its separation from the American Lung Association (ALA), resulting in the Society's independence. The seeds of the separation were sown over the course of many years. The fundamental reason driving the separation was the organizational structure of the ALA, with the ATS being a division within the larger organization and having neither the standing to make independent decisions nor the ability to respond effectively to the expectations of a growing and diverse membership. Additional important factors included continual organizational conflicts; ongoing struggles over finances; reluctance by the ALA to provide what the ATS considered to be appropriate support for research; divergence of areas of interest as the Society became more broad based to include critical care and sleep medicine, as well as concerns with medical practice issues; and internationalization of the Society, with an increasing proportion of members residing outside the United States. Once it was decided that the ATS could only exist as an independent organization, the separation agreement was negotiated in less than 3 years. Although there were substantial unknowns immediately after the separation, a unified leadership, a strongly supportive membership, and a skilled and dedicated staff guided the organization through this difficult period, from which the Society emerged as a strong independent professional organization that remains true to the public-minded spirit that guided its formation 107 years ago.