Founded in 1905 as the American Sanatorium Association, the American Thoracic Society is the world's leading medical society dedicated to accelerating the advancement of global respiratory health through multidisciplinary collaboration, education, and advocacy. Core activities of the Society’s more than 16,000 members are focused on leading scientific discoveries, advancing professional development, impacting global health, and transforming patient care. Key areas of member focus include developing clinical practice guidelines, hosting the annual International Conference, publishing four peer-reviewed journals, advocating for improved respiratory health globally, and developing an array of patient education and career development resources.

The American Sanatorium Association was established during a period when sanatoriums were beginning to multiply. In view of the fact that the members of the American Sanatorium Association were among those most influential in organizing the National Tuberculosis Association in 1904, membership in the latter organization was included as a requirement for membership in the American Sanatorium Association.

This form of relationship persisted, and the program of the American Sanatorium Association was developed to include much more than the sanatorium aspect of the treatment and prevention of tuberculosis. In 1938 it was deemed wise to acknowledge these larger interests by broadening functions, increasing activities and enlarging membership.

With these objectives the American Trudeau Society was established as the successor to the American Sanatorium Association and as an integral part of the National Tuberculosis Association, entrusted with its medical program.

To provide for these more comprehensive objectives, the constitution and bylaws of the American Sanatorium Association, as adopted originally December 1, 1905, and amended December 5, 1911, June 19, 1923, May 6, 1924, May 7, 1930, and April 22, 1936, were repealed, and a new constitution was adopted in Boston, Massachusetts, on June 26, 1939. It was amended in Philadelphia, Pennsylvania on May 6, 1942, New York City, N.Y. on June 15, 1948, and April 25, 1950 in Washington, D.C.

On May 26, 1952, the Bylaws were amended to provide for determination of Society dues by the membership on recommendation of the Council.

On May 18, 1954, the Bylaws were amended to increase the number of committees from five to seven and to increase the editorial board from nine to twelve members.

A new set of bylaws was adopted at the Annual Meeting in Milwaukee, Wisconsin, on May 24, 1955, which revised and combined the provisions of the old constitutions and bylaws. As part of this revision the constitution was legally discontinued on May 22, 1956 in New York City.

On May 7, 1957, the Bylaws were amended to provide for an enlarged Council consisting of the present Councilors-at-Large and a Representative Councilor from each state Trudeau Society.

On May 26, 1959, the Bylaws were amended to extend the qualification for membership to applicants with a Ph.D. or equivalent degree and provision was made for an Associate Membership for residents and fellows.

On May 17, 1960, the Bylaws were amended to change the name of the Society to American Thoracic Society to further extend its broadening interest and functions.

On May 22, 1962, the Bylaws were amended to provide that any member whose dues are in arrears for one year shall be dropped from membership in the Society unless the Council, after investigation, decides otherwise.

On May 26, 1964, the Bylaws were changed to provide honorary members with a subscription to The American Review of Respiratory Disease without any cost.

On May 24, 1966, the Bylaws were amended to update the document in line with the present activities of the Society.

On May 21, 1968, the Bylaws were amended to restate the objectives, to provide opportunities for the membership to have an increasing role in the management of ATS, and to strengthen the organization in the conduct of its business.

On May 26, 1969, the Bylaws were amended to provide for the creation of Scientific Assemblies, establish minimum standards for Chapters to be eligible for Council representation streamline membership approval mechanisms and make medical students eligible for membership.

On May 26, 1970, the Bylaws were amended to ease Associate Membership procedures for medical students, provide for absentee ballots in voting for officers, limit membership to one Scientific Assembly at any one time, and clarify the Bylaws amendment process.

On May 19, 1971, the Bylaws were amended to allow nurses and other highly qualified health professionals who are active in the respiratory disease field to become members of the Society and to provide that Associate Members may be considered for membership in a Scientific Assembly.

On May 24, 1972, a new set of bylaws was adopted containing only the basic principles of operation of the Society and giving more latitude to the governing body. Revisions included reference to ATS as a scientific rather than medical society, election of Honorary Members by Council, deletion of the corresponding and inactive membership categories, provision for a second Representative Councilor for qualified Scientific Assemblies, an Annual Meeting quorum of 50 rather than 100, more flexibility in naming committees, and provision for submitting substance of proposed bylaws amendments so membership will have privileges of making editorial changes.

On May 13, 1974, the Bylaws were amended to provide for the change of names to American Lung Association and Congress of Lung Association Staff, and the replacement of the editorial board of the official journal with the ARRD Policy Committee.

On May 16, 1976, provision was made for a standing Publications Policy Committee to consider the broad policy questions relative to all current ATS periodical publications and also to recommend, when appropriate, the development of new publications. The new committee incorporated into its structure the previous ARRD Policy Committee.

On May 18, 1977, the Bylaws were amended to clarify the role of the voting and non-voting (ex-officio) members of the Publications Policy Committee in the procedure on appointment and evaluation of editors.

On May 19, 1980, the Bylaws were amended to provide for the establishment of a new governing body, referred to as the Board of Directors, and the formation of a forum for Chapter Representative Councilors, referred to as the Council of Chapter Representatives. The sequence of Bylaws' Articles was changed to facilitate continuity. Minor editorial revisions were made to provide greater uniformity.

May 8, 1988, the Bylaws were amended to include the ALA President, President-Elect, and Past President as members of the ATS Board of Directors, and to designate the ATS Immediate Past President as an officer of the Society. Minor editorial revisions were made to provide greater uniformity.

On May 19, 1992, the Bylaws were amended to change the membership of the Board of Directors, to change the definition of SENIOR member, to establish a category of EMERITUS member and to establish an AFFILIATE category.

On May 22, 2001, the Bylaws were amended to clarify the roles of the following committees Ad-hoc, Other, Executive, Nominating and Audit and Finance.

On May 20, 2003, the Bylaws were amended to include a provision, granting the Board of Directors the authority to approve compensation to the President for their services and related administrative expenses.

On May 25, 2004, the Bylaws were amended to revise the purpose statement; the addition of a new member category (In-Transition); the addition of two presidential appointees to the Board of Directors; and greater clarity on the transition of the members of the ATS Executive Committee.

On May 24, 2005, the Bylaws were amended to include a provision, granting the Board of Directors the authority to approve compensation to the President-elect for their services and related administrative expenses. Additionally, the composition of the Board of Directors was revised to include the Chair of the Foundation of ATS and the Chair of the Public Advisory Roundtable.

On May 19, 2009, the bylaws were amended to update the purpose statement to include sleep-related.  Additionally, the composition of the Board of Directors was revised to remove the two ALA representatives and CLAS representative.

On May 17, 2011, the bylaws were amended to reflect the new membership categories that were approved by the Board of Directors in August 2009.  The composition of the Board of Directors was revised to include the Education Committee chair and the International Conference Committee chair.  Additionally, the process by which future bylaws amendments are approved was revised to allow for electronic voting.

On May 23, 2017, the bylaws were amended to provide greater consistency in the work of ATS committees; and uniformity of the leadership role on committees.  Additionally, the Gross National Product language was revised to align with the World Bank definition.