The Main Newsletters Series comprises the primary house organ for the company, in all versions over time, from 1916 through 1986, when JWT became a unit of the WPP Group. The newsletter addressed issues of importance to the entire company, with articles on account news, client lists--or account gains and losses--and biographies and short notes on JWT staff, including professional accomplishments, promotions and transfers, visits to other JWT offices, and personal events (i.e. marriages, births, and deaths). The series also documents the results of both general and client-specific market research surveys, as well as general discussions of various markets and industries; television, radio, and print media developments (sometimes including listings of programs sponsored by JWT clients); and news from and profiles of JWT's offices and divisions around the world.

There are some gaps in publication of these newsletters, most notably 1931-1945 and 1970-1975. Coverage of international affairs varies substantially, though all of the titles in this series provide some news from JWT's offices overseas. The richest sources of JWT international news are the newsletters of the 1970s and 1980s, when there is a substantial increase in the frequency and depth of attention paid to JWT operations globally. See also the International Newsletters Series. One particularly useful source is "Thumbnail Sketches," a column published regularly in the newsletter from 1946 to 1964 which profiled JWT staff. Also common were reports on JWT advertising campaigns and their subsequent impact on both the market and the client; from 1946 until roughly 1962, the newsletters featured the "Campaign of the Week," detailing particularly successful campaigns. A listing of "Campaign of the Week" topics appears at the end of the finding aid.

The newsletters in this series were all published by the New York office, sometimes with local office newsletter inserts (see the Domestic Newsletters Series: Offices Subseries and the International Newsletter Series); copies of advertisements or management correspondence were sometimes attached as well.

The newsletters are organized chronologically by the date range of publication. Folders containing correspondence relating to newsletters precede the listing of newsletter titles.