[Excerpt] This report presents data on Member tenure and a historical analysis of tenure trends. During the 19th century, the average service of Representatives and Senators remained roughly constant, with little or no change over time; the average years of service was slightly higher for the first half of the century than during the second. During the late 19th and through the 20th century, the average years of service for Senators and Representatives steadily increased. The report also examines two further issues related to Member tenure: the distribution of Member service that underlies the aggregate chamber averages and historical trends in the percentage of Members who have served in both chambers. Although the average service tenure of Members has increased, more than half of Representatives and nearly half of Senators in recent Congresses have served eight years or less. While only a small and declining proportion of Representatives have historically had previous Senate experience, throughout history a sizeable percentage of Senators have previously served in the House.