This report presents a profile of the membership of the 115th Congress (2017-2018) as of October 1, 2018. Statistical information is included on selected characteristics of Members, including data on party affiliation, average age, occupation, education, length of congressional service, religious affiliation, gender, ethnicity, foreign births, and military service. In the House of Representatives, there are 237 Republicans (including 1 Delegate and the Resident Commissioner of Puerto Rico), 197 Democrats (including 4 Delegates), and 7 vacant seats. The Senate has 51 Republicans, 47 Democrats, and 2 Independents, who both caucus with the Democrats. The average age of Members of the House at the beginning of the 115th Congress was 57.8 years; of Senators, 61.8 years, among the oldest in U.S. history. The overwhelming majority of Members of Congress have a college education. The dominant professions of Members are public service/politics, business, and law. Most Members identify as Christians, and Protestants collectively constitute the majority religious affiliation. Roman Catholics account for the largest single religious denomination, and numerous other affiliations are represented, including Jewish, Mormon, Buddhist, Muslim, Hindu, Greek Orthodox, Pentecostal Christian, Unitarian Universalist, and Christian Science. The average length of service for Representatives at the beginning of the 115th Congress was 9.4 years (4.7 House terms); for Senators, 10.1 years (1.7 Senate terms).