This series focuses upon the Northern Ireland conflict, commonly referred to as "The Troubles," which was a 30 year conflict fought between Nationalists (mainly self-identified Irish or Roman Catholics) and Unionists (mainly self-identified British or Protestants). It contains information relating to numerous subjects including, but not limited to: Armagh prison, Long Kesh prison, British reports on Northern Irish terrorist activities, anti-Margaret Thatcher and anti-British propaganda, news coverage of the Provisional Irish Republican Army's (IRA) assasination of Lord Louis Mountbatten, Bloody Sunday, the trial of John DeLorean, MacBride Principles, plastic and rubber bullets, as well as human rights in Northern Ireland.

The Jack O'Brien Papers contains a large volume of material related to the Troubles, but within this series, it became evident that four categories featured more heavily than others. To reflect this, specific sub-series focusing upon the 1981 Hunger Strike, Irish American Organizations, the U.S.-U.K. Extradition Treaties, and news coverage of the Troubles have also been created.

Materials in this series include correspondence, flyers, newsletters, photographs, speeches, official reports, Congresssional Records, press releases, interviews, book excerpts, posters, audio cassettes, and newspaper clippings.

This series focuses on Northern Ireland after the signing of the Good Friday Agreement in 1998. This agreement ended most of the violence in Northern Ireland and is considered the end point of the Troubles. This series focuses upon efforts towards a united Ireland, Brexit, Sinn Fein, as well as the legacy of the Troubles such as the arrest of Gerry Adams for the murder of Jean McConville and new evidence regarding the murder of Patrick Finucane. This series also contains papers related to the Commission on Security and Cooperation in Europe (CSCE), also known as the U.S. Helsinki Commission.

This series contains newsletters, correspondence, official reports, news clippings, press releases, posters, booklets, calendars, Congressional Records, book excerpts, emails, flyers, bumper stickers, brochures, and Good Friday Agreement commemoration materials.

This series focuses on Boston College's 2001 "Belfast Project," which was an oral history project focused on the Troubles. The Belfast Project interviewed former Provisional IRA members such as Dolours Price and Anthony McIntyre, both of whom recounted their experiences in the IRA. This series mostly contains materials related to the 2011 controversy surrounding the Police Service of Northern Ireland (PSNI) and British government subpoenaing the Belfast Project's transcripts in connection with the abduction and murder of Jean McConville in 1972. The series documents the outrage experienced by the Irish American community and supporters of Boston College by the PSNI and British government's actions, as well as the legal ramifications of the subpoena.

This series contains newspaper clippings, correspondence, legal documents, emails, press statements, and memorandum.

This series focuses upon Jack O'Brien's involvement and interest in monuments commemorating Irish individuals, as well as important events in Irish history. Topics include, but are not limited to the establishment of Irish Brigade monuments at Gettysburg and Antietam, the General Thomas Francis Meagher monument, creation of Robert Emmet Park, as well as the Commodore John Barry Memorial and Barry Gate at the U.S. Naval Academy in Annapolis, Maryland.

Materials in this series include emails, fundraising financial logs, postcards, correspondence, flyers, architectural drawings, commemorative programs, photographs, brochures, newsclippings, CDs, VHS tapes, DVDs, a small sculpture, banners, flags, and posters.

This series focuses upon the history, activities, and legacy of the Ancient Order of the Hibernians (AOH), as well as Jack O'Brien's involvement with this organization. Materials include official memorandum, newsletters, AOH election materials, social invitations, emails, correspondence, posters, DVDs, booklets, photographs, commemorative coin, badges, convention materials, press releases, documents related to the Ladies Ancient Order of Hibernians (LAOH), as well as copies of the National Hibernian Digest, the official newspaper of the Ancient Order of Hibernians.

This series reflects Jack O'Brien's interest in Irish history and focuses on many topics such as the 1916 Easter Rising, Fenian movement, the Great Famine in Ireland, the role of Irish and Irish American citizens during the American Civil War, the history of Irish and British relations, John F. Kennedy, World War I, and Grosse Ile (a Canadian Island that served as a refuge for Irish immigrants escaping the Great Famine).

Materials in this series include brochures, news clippings, magazine articles, photographs, booklets, a DVD, and posters.

This series contains personal materials related to Jack O'Brien and focuses on subjects like O'Brien's family history, his interest in Irish culture, as well as his support of Irish cultural organizations and institutions.

Materials include correspondence, St. Patrick's Day Parade magazines, Jack O'Briens 2015 St. Patrick's Day Parade Grand Marshal magnet, Irish Heritage Festival magazines and flyers, brochures, papers belonging to Irish American organizations, programs, booklets, DVDs, newspaper clippings, emails, photographs, posters, stickers, vinyl records, business cards, buttons, and newsletters.