Elected politicians employ in their personal offices a wide range of assistants who support them in their political work within the legislature as well as the executive. In the past decade or so the study of ministerial political advisors has received attention in numerous Westminster-style countries, including Canada, especially in regards to their relationship with the professional public service. However, very little research has considered the work of political staffers who support elite political actors within the legislature rather than within the executive. This is a significant gap. For example, there are 338 elected Members of Parliament in Canada, all of whom are entitled to hire political staff to perform a variety of duties—from office administration such as scheduling and managing expense claims to research and policy analysis, communications and engagement with lobbyists and constituents-- in both their parliamentary and local offices. Political staffers also provide similar support (with the exception of constituency work) for 105 unelected Senators. Altogether, the total complement of parliamentarians’ political staff may outnumber ministerial staff by three or even four to one. While they do not exercise direct input on government policy and activity, parliamentary staffers, through their privileged access to MPs and Senators, have the potential for influence in different ways. Opposition staffers will likely have more opportunity to advise on policy or legislative tactics, but staffers from all parties will have influence with respect to caucus dynamics, local activities and controlling access to parliamentarians by outside stakeholders, including constituents and lobbyists. Yet they usually do so outside of the accountability framework applicable to most other public office holders. Political staffers working in parliamentary caucus research offices are an important subset of legislative staffers seldom examined in academic literature. Since 1969, the Canadian House of Commons has provided funding for a caucus research office to each recognized political party based on its share of seats. This support is especially important for the leaders of opposition parties who, unlike the prime minister and other government ministers, have no access to the public service and few other resources for policy and communications work. Based on survey responses and elite interviews, this paper profiles the nature and function of the caucus research offices for three Canadian political parties, namely the governing Liberal Party, the Official Opposition Conservative Party and the third place New Democratic Party, and considers questions such as their relationship with the caucus and leader, the nature and range of services and products offered, and the differences of approach between the three parties.