As well as original and photocopied research materials, the subseries includes cross-reference sheets pointing to relevant information organized elsewhere in Subseries B. Subject Files or Subseries C. People Files, and photographic prints including those used in Partners in Business. The latter sometimes include photographic negatives, and information on sources, permissions, and placement in the book's final layout.

The files give an overview of the evolution of Brown Brothers from a commodities importation firm to a highly influential worldwide bank and investment house. Important events and topics include agent Joseph Shipley's negotiations with the Bank of England during the panic of 1837; bank actions during the panics of 1857 and 1907 and its contributions to the Gold Fund of 1914; funding actions in Nicaragua from 1911 on, and subsequent investigations of its political consequences; Brown Brothers' relationship and eventual merger with the Harriman interests; changes in partnership agreements and personnel; loans and bond issues; and the firm's interest in and promotion of its history through its anniversary celebrations at 100, 125, and 150 years.

Materials dating after the 1940s contain more information about the daily administration of the bank, including photographs of current employees and production of the 1959 brochure "Personality of a Bank". Many materials from the mid-1950s appear to have been taken from the scrapbooks of Catherine Barrett (see Series VI. Scrapbooks and Collected Material). From 1964 to 1968 John Kouwenhoven was a Brown Brothers Harriman staff member. The files from that period, including information routinely routed to the Historical Files about the firm's day-to-day operations, policy, and personnel changes, provide a look at business practices of this period. The files also document Kouwenhoven's activities in interviewing current and past employees and partners, and establishing procedures for his office.

The material in this subseries complements and often duplicates that in the other three subseries of Series I. For example, material on the 150th anniversary celebrations occurs here under "1968" and in the Subject files under both "Sesquicentennial" and "Sun Valley".

The subseries is arranged chronologically but, within this order, some materials are grouped by subject. These have been inserted at their beginning dates and the chronological order resumes at their completion. They include information on Brown Brothers & Co.'s involvement in Nicaraguan financing, 1911-1929, which follows 1910-1914; the 1914-1918 partner deliberations on separating the business of Brown Shipley & Co. from that of Brown Brothers & Co., which follows 1917; the merger of Brown Brothers & Co. with W.A. Harriman (1928-1935), which follows 1931; the preparation and publication of the brochure "The Personality of a Bank", which follows 1959; funding of Community Research & Development /Rouse Corporation /Columbia MD, which precedes the 1965 files; and the company's 150th anniversary, which follows the other 1968 files.

Duplication of materials is prevalent. For example, a set of Partners' letterbooks, 1851-1859, was photocopied from microfilm housed at the Liverpool Public Libraries. The 1851-1853 letters were also photocopied, individually foldered, and annotated by Kouwenhoven. These are now arranged by date and each letter is preceded by a photocopy of the annotations.

Bound volumes 1-6 are listed together at the end of the series, in chronological order.

Various oversize photographs found organized separately in the Records, but originally marked as belonging to the Chronological files, are included here.

The subseries documents Brown Brothers Harriman and its predecessor companies' internal and external connections with correspondent banks and branch offices, as well as with organizations, investors, and individuals worldwide. They provide information on its offices, activities, and agents, including investment in the Collins steamship line and the deaths of Brown family members aboard Arctic in 1854; details of the 1931 merger with the Harriman interests; deeds, plans, and purchases of property at and around the firm's New York offices at 59 Wall Street; and financing during World Wars I and II. The co-partnership files give details of the additions to the firm's partners, and their loss through retirement or death, from 1915 to 1953.

Highlights include detailed examples of Brown Brothers & Co.'s letters of credit, which provided access to funds for individuals and organizations internationally, including a list of London locations that would cash travelers checks with an accompanying note from John D. Rockefeller Jr.; W. Averell Harriman's unused $10,000 letter of credit while he was roving ambassador for President Franklin Roosevelt in 1942; and, from the Philadelphia office, a credit draft endorsed with withdrawals from Hawaii through South and East Asia to France and Italy on a 1928 world tour by a Brown Brothers customer. An indexed collection of letter abstracts and other communications received and sent by the Philadelphia office of Brown Brothers & Co. provides a snapshot of bank operations nationally and internationally, including foreign exchange issues, in the period 1885-1904.

The subseries is arranged alphabetically by name of person, place, event, or other appropriate subject heading.

Placed before the alphabetical listing (which begins with "Alex. Brown & Sons") is a group of Case History files, which were prepared for inclusion in Partners in Banking, but not eventually used in that format. Information from these proposed Case Histories on the merger of Bangor Aroostook Railroad with the Punta Alegre sugar manufacturing company, and Brown Brothers Harriman's role in the development of Columbia, MD, became instead extended captions describing photographs at the end of the book (pp. 206-208). Original order of these materials has been retained.

The organization of materials in the subseries is not always consistent, and is often duplicative. For example, information on overseas banks is grouped into Foreign Banks, but there are separate files for Banque de France and Norge Bank; information on Punta Alegre exists in both the Case Files and in alphabetical order; and materials pertaining to the firm's 150th anniversary celebrations are included under both "Sesquicentennial" and "Sun Valley", as well as in the "1968" materials in Subseries I.A. Chronological Files. Material originally filed under "Metropolitan Museum of Art" has been included in the folder "Crosby Brown Collection of Musical Instruments," because it is specifically on that subject. Consulting the card catalog to the collection available in the Reading Room, which provides item-level indexing, may be helpful in resolving these inconsistencies.

Materials within subject headings were originally in chronological order, and that has been retained in smaller files. In larger files, materials have been organized into types (e.g., clippings, correspondence, cross-reference sheets, images) for clearer identification, and then ordered chronologically.

Volumes 7-12, which were originally included in the Subject files, have been removed and are listed in chronological order at the end of the container list.

All information pertaining to Brown Brothers' Wall Street offices, which was originally out of order (including a chronology found together with some visual materials), is now included in the "Property" files. Correspondence between partner Thatcher Brown and Museum of the City of New York director Harding Scholle from the 1940s indicates that the original deeds to the Wall Street property from 1699 and 1708 are on permanent loan to the Museum, available at that time to be borrowed on request.

Various materials found elsewhere in the collection have been added to the Subject files as appropriate. Binders containing draft and final data printouts with information on attendees at the 1968 Sun Valley sesquicentennial gathering are now included in the "Sun Valley" materials as boxes 55-57. Their date order is not consistent because these materials are housed in different-sized boxes.

Records almost exclusively to do with co-partnership agreements had been culled from the firm's original records for inclusion in Thatcher Brown's 1950 book Brown Brothers & Co. [and] Brown Brothers Harriman & Co., 1900-1950. They were then further culled in early June 1964 and were labeled as awaiting John Kouwenhoven's return to be reviewed.

Some files labeled as originating from the Tax Department are now included under that designation. General files from the Department are in chronological order, followed by client-specific folders in alphabetical order by last name. Information in them includes some of the individuals also represented in Subseries I.C. People.

Two books of stockholder records for Wall and Hanover Street Realty Co. are included as Volumes 9 and 10. Folders of Brown Bros. & Co. correspondence marked with Kouwenhoven's Subject designation, but not included in the original filing cabinets and not annotated, have been added there.

Extracts of letters and other communications compiled into a volume (with index), which became disbound and is labeled in Kouwenhoven's handwriting as having originated from the Philadelphia office, is now included with those materials. There is some variation in the box order of these items because they are housed in different sized boxes

Various oversize photographic materials found organized separately in the Records but originally marked as belonging to the Subject files are now included here. Two photographs of lower Manhattan showing the Brown Brothers building at 59 Wall Street were not labeled with a subject heading; these have been added to the "Property" files.