From the press release:
The U.S. Government Publishing Office (GPO) makes available the authentic, digital version of the official directory of the 115th Congress.
Mandated by Title 44 of the U.S. Code, the Congressional Directory is prepared by GPO under the direction of the Joint Committee on Printing (JCP). More than just a guide to Members, committees, and officials of the 115th Congress, the Congressional Directory is the only document issued by Congress that shows the overall organization of the two chambers and their committees, offices, and support organizations.
The Directory includes historical statistics, information on the Capitol buildings and grounds, and a guide to the other agencies of the Legislative Branch. In addition, the Congressional Directory provides information on the departments and agencies of the Executive Branch, the U.S. Courts, international organizations, foreign diplomatic offices in the United States, and members of the congressional press, radio, and television galleries…..