CONTEXT:Advance care planning (ACP) engagement includes a wide range of behaviors and actions related to discussions and documentation, yet few ACP intervention studies measure the full process. OBJECTIVES:The objective of the study was to compare the effects of an easy-to-read advance directive (AD) versus an ACP web site plus the AD (PREPARE + AD) on Behavior Change Processes and Actions, including discussions and documentation. METHODS:Secondary data were from a completed ACP trial. Participants were primary care patients, ≥60 years old, with two comorbidities. We used the validated ACP Engagement Survey to examine six-month change in subscales measuring Behavior Change Processes (knowledge, contemplation, self-efficacy, readiness) and Actions (decision makers, quality of life, flexibility for decision makers, asking clinicians questions), specifically related to discussions and documentation. We used adjusted mixed-effects linear models to compare mean change and engagement over time. RESULTS:Compared to the AD-only, PREPARE + AD resulted in greater increases in all Behavior Change Processes subscales and Actions related to decision makers, quality of life, and flexibility (all P-values ≤0.005). Both interventions significantly increased the proportion of participants who engaged in ACP discussions (PREPARE + AD, 99.5%; AD-only, 93.3%) and documentation (PREPARE + AD, 99.5%; AD-only, 90.4%), with greater increases for PREPARE + AD (all P-values <0.001). CONCLUSION:Both PREPARE plus an easy-to-read AD and an AD-only markedly increased ACP engagement in a full range of ACP behaviors, including discussions and documentation, and engagement was nearly 100% with PREPARE + AD. Future ACP studies should examine a full range of ACP behaviors beyond ADs and the impact of PREPARE and easy-to-read AD implementation on health care systems.