Significant progress has been made in the area of adhesives in restorative dentistry. With respect to composite restoratives, bond strengths greater than the targeted 17 MPa are now routinely achieved by modern dentin bonding systems in laboratory tests. Each adhesive system must be handled according to the manufacturer's instructions and with careful attention to the details of application for maximal success. Clinical documentation of the success of the modern systems is limited. This especially true for the multipurpose applications often advocated by the product instructions or clinicians lecturing from personal anecdotal experience. The confirmation of laboratory results with controlled clinical trials often occurs late or not at all. A thorough understanding of the in vivo performance is needed to gain the knowledge necessary to further the technologic advances in this area.