Background: Operating room to intensive care unit handoffs are high-risk events for critically ill patients. Studies in selected patient populations show that standardizing operating room to intensive care unit handoffs improves information exchange and decreases errors. To adapt these findings to mixed surgical populations, we propose to study the implementation of a standardized operating room to intensive care unit handoff process in two intensive care units currently without an existing standard process. Methods/Design: The Handoffs and Transitions in Critical Care (HATRICC) study is a hybrid effectiveness- implementation trial of operating room to intensive care unit handoffs. We will use mixed methods to conduct a needs assessment of the current handoff process, adapt published handoff processes, and implement a new standardized handoff process in two academic intensive care units. Needs assessment: We will use non-participant observation to observe the current handoff process. Focus groups, interviews, and surveys of clinicians will elicit participants’ impressions about the current process. Adaptation and implementation: We will adapt published standardized handoff processes using the needs assessment findings. We will use small group simulation to test the new process’ feasibility. After simulation, we will incorporate the new handoff process into the clinical work of all providers in the study units. Evaluation: Using the same methods employed in the needs assessment phase, we will evaluate use of the new handoff process. Data analysis: The primary effectiveness outcome is the number of information omissions per handoff episode as compared to the pre-intervention period. Additional intervention outcomes include patient intensive care unit length of stay and intensive care unit mortality. The primary implementation outcome is acceptability of the new process. Additional implementation outcomes include feasibility, fidelity and sustainability. Discussion: The HATRICC study will examine the effectiveness and implementation of a standardized operating room to intensive care unit handoff process. Findings from this study have the potential to improve healthcare communication and outcomes for critically ill patients. Trial registration: ClinicalTrials.gov identifier: NCT02267174. Date of registration October 16, 2014.