This chapter provides an introduction to the section dealing with oral transmucosal drug delivery. It starts with a historical perspective of the use of this route, and then some of the advantages and disadvantages are presented. Next, the structure of the oral mucosa and the pathways for drug absorption are briefly described. Some problems inherent in using isolated tissues for permeation experiments are mentioned and some common misconceptions are noted. A brief overview of some of the buccal/sublingual drugs on the U.S. market provides a snap shot of where we are today. The chapter also gives some insight into the difficulties encountered in developing these products. Lastly, it attempts to give an indication, in broad terms, of the progress that is likely to be made in this area of drug delivery and an assessment of the potential, in the authors’ view, of the future of buccal and sublingual drugs.