The documents in this series represent the Congresses somewhat unevenly. The XXIV Congress held in Washington, D.C. in 1968 is most comprehensively documented. The files of the earlier Congresses are less complete.

By the nature of the IUPS it is obvious that some correspondence in the Congresses Series and some in the Executive/Council Series could be interchangeable. In some instances a letter was found to be in both files. Rather than solve an organizational imponderable, the rationale of the files' organization was to accept what had been received as Congresses correspondence, as a Congress document, even though it could also have been an Executive/Council document.

Otherwise the Congresses files, expand or not, as the existing material may or may not permit division into various subdivisions, such as:

Initially, this series contains material about member organizations, such as correspondence, activities and background information. However, it is not limited to members, but includes "supporting societies" and any organization or body that has a declared interest in the work of the congresses. In some instances those bodies are themselves other scientific unions. Material pertaining to IUPS Regional Meetings and/or Symposia that appear to be inspired by the activities of the Adhering Society or Supporting Society and are not clearly a part of a congress are also organized in this series.

Those symposia or satellite meetings or even regional meetings that appear to be clearly a part of a congress are filed together with that congress.

The United States is represented in the Adhering Societies/Union International Unions series under the heading: U.S. Committee. In fact, the U.S. Committee appears to be a function of the National Academy of Sciences, which technically would be the Adhering Society. The National Academy of Sciences, however, appears to have considerable expanse in its interests. Therefore, in order to collect the substantive aspect of the participation as a member of the IUPS, there is simply a file section titled "U.S. Committee" in this series.

Based on earlier statements about the "Permanent Committee," this series begins with the files of the "Permanent Committee."

Unfortunately, most of the material in the Executive/Council Series has been signed without the title of the author. It is apparent, in the case of some individuals, that they held more than one office at various times. Without an inscribed title under their name, their office at the time of writing is not necessarily known. Therefore, this series is mostly a chronological correspondence file.

There did emerge from this material certain documents that were easily categorized. They are:

Archivist's files and a publication called "Newsletter" material are also filed under their separate identities in the Executive/Council series. These were included because their functions appear to be the responsibility of the Executive/Council whether or not the offices of the Archivist and Editor of the Newsletter were in themselves necessarily Executive Committee or Council positions.

The Executive/Council series does not include the correspondence of the officers of a particular congress, since each congress has its own officers named for that Congress only.

The Congresses and/or the Executive/Council established various commissions or committees for specific purposes. While the commission or committee may report in due course to a congress or to the Executive/Council or both, some function in a time span greater than a congress or an Executive/Council meeting. Hence, this work was collected in a separate series whenever the commission or committee was seen to be established by the IUPS.

Items relating to a committee or commission which appeared to be established by an Adhering Society or equal were filed together with the Adhering Society in Series II.

In some instances, congresses were commemorated with photographs which in themselves are not the content of the congress or about the bureaucratic activity of the congress, such as the correspondence may be, but simply a visual record of the culture of the congress.

Hence, photographs of all congresses have been collected under a separate series and are not included in the Congresses Series.

Sometimes other meetings or individuals in the IUPS are also documented in photographs. Therefore, the Photographs Series is further divided into subseries.

This series contains books, papers or statements which record collective histories or selective histories of the IUPS.

Contains background on the incorporation of the IUPS, its Constitution, By-Laws and Statutes.

The congresses were also commemorated with medals, cultural programs, tours, and the like which, like the photographs, are not directly the content of the congress, but are part of the experience of attending a congress. Like the photographs, these materials and objects have been collected in their own series.

This series contains correspondence and other material that had been bound together (before the archives came to the American Philosophical Society) and such collected information that would have been otherwise filed under other series. Archivists at the APS decided not to disbind these volumes and file the documents into their proper places in the series described above, so it is therefore necessary to use the contents of these bound volumes in conjunction with related documents from other series.