Receptor occupancy (RO) studies have long been used to demonstrate target engagement of therapeutic antibodies. Today, many programs rely on RO data to inform dose selection, pharmacodynamic interpretation, biomarker strategy, and mechanism-of-action assessments. Bispecific antibodies, T-cell engagers, antibody-drug conjugates (ADCs), and other next-generation therapies have expanded both the opportunities and complexities associated with receptor occupancy assessments [1].