Women in US jails have many social and health risks that merit attention from public health agencies. This article: (1) reviews national and local data on this population for indicators of social disadvantage and of several health risks/conditions (substance abuse, risky sex, and mental illness), (2) describes the impact of federal mandatory sentencing for drug violations and recent developments in states on the numbers of incarcerated women, (3) outlines the similarities and differences between jails and prisons, focusing on characteristics of jails that facilitate and constrain intervention and evaluation activities, and (4) adds lessons learned in six years of experience in county and state jails in Texas.