Criminal justice reforms in the past two decades have significantly reduced the number of juveniles (under age 18) detained in adult correctional facilities; however, individuals in their late teens and early twenties, often referred to as emerging adults (EAs), face disproportionately high rates of incarceration in jails, accounting for nearly 26% of the jail population. The present chapter reviews and synthesizes what is known about EAs regarding their psychosocial and cognitive development, mental health and treatment needs, and risk for behavioral problems while detained. We highlight promising research on interventions and assessment strategies for EAs in jails and discuss a pertinent case example with related practice considerations. Given the recent advocacy efforts and subsequent policy changes that have begun to alter the sentencing and treatment of EAs who come into contact with the justice system, it is imperative that researchers continue to investigate best practices for meeting this population’s unique needs.