Although weekly or twice-weekly treatment of posttraumatic stress disorder (PTSD) using interventions such as Cognitive Processing Therapy (CPT) has been shown to be highly effective, recent research suggests that increasing the session frequency can both help individuals experience more rapid symptom improvements and complete a full course of treatment. In massed CPT, individuals receive multiple sessions per week or multiple times per day. Massed CPT can be delivered on its own or in combination with adjunctive services as part of more comprehensive massed treatment programs. Participation in massed CPT has been shown to produce large and lasting symptom and functional improvements in individuals with PTSD in as little as 1–3 weeks when compared to 3–4 months in once-weekly CPT. Massed CPT is also associated with high completion rates of around 90%, suggesting that most individuals who start treatment receive a full dose of the intervention. Moreover, massed CPT has been shown to be effective across a wide range of populations, trauma types, and even co-occurring conditions. This chapter summarizes the current literature on massed CPT and discusses clinical applications of the intervention via a case example.