PROJECT SUMMARY/ABSTRACT Medication adherence is a current scientific priority of the National Cancer Institute and a top priority in clinical trials. Electronic adherence monitoring devices (EAMDs) are pill bottles or boxes that contain a computer chip that records the dates and times of each bottle/box opening (or “actuation”). Due to their accuracy and ability to capture day-to-day medication-taking behavior, EAMDs are increasingly cited (i.e., by the FDA) as the preferred measure of daily anticancer medication adherence in research. Unfortunately, researchers currently lack the tools they need to accurately and efficiently convert raw EAMD actuations into adherence data and current methods of completing this task are unstandardized, error-prone, and burdensome. The purpose of this R21 is to develop a novel algorithm to convert EAMD actuations into adherence data. To maximize potential uptake and usability, we will engage a multidisciplinary adherence science focus group to inform the design of the algorithm and associated user interface (Aim 1). We will then evaluate the accuracy of the algorithm in classifying daily adherence data (Aim 2) and obtain quality of use feedback (Aim 3) to inform final refinements prior to large-scale testing.