This chapter gives only a very brief overview of some of the basic characteristics of adhesives related to the mechanical strength and performance of adhesive connections. The rate of separation also becomes important and it introduces additional theoretical complexities in understanding the finer points of adhesion when the two solids behave in a tacky manner. The term "frozen" in the science of adhesion reflects the existing, initial state of stress due to the external, rather than the internal, constraints. The mechanism of adhesion helps to distribute and mitigate stress concentrations commonly found in bolted, riveted, and welded joints. The technology of adhesion is concerned with the analysis of forces existing between the adherends and the adhesives. Solid-to-solid adhesion results from the pressing together of the two surfaces in a vacuum. The design of lap joints depends on the knowledge of the adhesives, as well as on the rigidity of the adherends.