“No-shows,” or missed visits are a persistent problem in all health care systems. They compromise patient access, lengthen wait times, increase health care inefficiencies, and worsen clinical care. The VA’s no-show rate has shown no improvement in years, resulting in a staggering nine million ambulatory no-shows in 2015 and perhaps over $1 billion in additional annual costs. Appointment reminders are an essential element to addressing no-shows but major research gaps exist. Behavioral economics (BE) suggests that “nudges” can be designed to make it easier for people to do the “right” thing while retaining individual autonomy. We draw from BE, psychology and related fields to identify concepts that can be applied to innovating the field of appointment reminders. One concept is social norms, which suggests that Veterans are likely to attend appointments if they sense that it is the norm for Veterans to do so. Another concept is based on the idea that providing clear instructions and an implementation plan increases the target behavior. A third approach is to highlight potential harms or losses to the Veteran from missing an appointment, while a fourth approach instead highlights potential negative consequences of no- showing to other Veterans. Each of these concepts can be transformed into messages that can be incorporated into appointment reminders. We will design and evaluate four intervention groups varying in type of nudge included in appointment reminder letters. We will address the following Specific Aims: 1) Develop and iteratively refine BE-informed messages based on Veterans’ perceptions, and incorporate them into enhanced appointment reminders; 2) Determine the effect of four versions of enhanced appointment reminders on measures relevant to treatment access, compared with usual reminders; 3) Evaluate differences in treatment effect associated with four versions of enhanced appointment reminders; 4) Characterize potential barriers and facilitators to widespread implementation of enhanced appointment reminder messages. Applying insights from BE to enhance appointment attendance in VA is highly significant and innovative. VA leaders describe reducing no-shows as critical to efforts to improve access, the top priority in VA. Appointment reminders are especially important in mental health (where no-show rates are high) and primary care (where appointments are scheduled far in advance). With the exception of a few studies in the U.K.’s National Health Service, BE has not been incorporated and evaluated in the design and content of appointment reminders. After iterative refinement of nudges to include in enhanced appointment reminders, we will conduct a cluster randomized controlled trial to test four interventions. Intervention arms will vary by what type of nudge and messages are added to appointment reminders. Appointments will be randomly allocated at the provider-level to one of the four interventions or a control group of usual appointmen...