As novel vaccine antigens and adjuvants are being tested in humans, understanding of critical quality attributes essential for eliciting optimal vaccine response and vaccine antigen-adjuvant interactions is pivotal for vaccine safety and eliciting 'protective' immune responses. Therefore, the efforts to better characterize and evaluate vaccine antigen and antigen-adjuvant drug products need to begin very early during the discovery and development phase. In this review, we discuss the importance of characterization of physicochemical and functional properties in vaccine antigen, adjuvant and the final antigen-adjuvant drug product and emphasize the greater need for more extensive understanding of vaccine antigen-adjuvant interactions. We highlight the key parameters and quality attributes that are critical to measure during preclinical and clinical testing of the vaccine and discuss in some detail the technologies, and their limitations, used in analyzing the key physicochemical and functional attributes of vaccine antigen and antigen-adjuvant drug product.