This issue of "Research Library Issues" ("RLI") presents three articles by Stanley Wilder in which he explores a series of trends shaping the professional population of Association of Research Libraries (ARL) member institutions. Wilder's articles serve as a powerful illumination of the demographic shifts taking place in the research library profession, where progress has been made towards realizing long-standing goals vis-à-vis diversity and inclusion, the closing of the income gap across racial and ethnic lines, and the lopsided nature of the age distribution curve…and the inevitable major correction that has already begun as older librarians reach a natural age limit on how long they can continue working. Articles include: (1) Demographic Trends in the ARL Library Professional Population: An Overview (Steven Mandeville-Gamble); (2) Delayed Retirements and the Youth Movement among ARL Library Professionals; (3) Hiring and Staffing Trends in ARL Libraries; and (4) Selected Demographic Trends in the ARL Professional Population.