Strong evidence exists demonstrating the benefits of tight glycemic control in type 1 and type 2 diabetes mellitus patients, but glycemic goals are not adequately achieved for many patients. Advancement in the knowledge surrounding the physiology of endogenous glucoregulatory peptide hormones, such as glucose-dependent insulinotropic polypeptide and glucagon-like peptide-1, has led to new therapeutic targets for the treatment of type 2 diabetes mellitus. Dipeptidyl peptidase-4 (DPP-4) inhibitors provide practitioners with a novel mechanism of action to use for combination therapies for the treatment of type 2 diabetes mellitus. This article, part 3 of a 3-part series, reviews the new class of medications known as DPP-4 inhibitors as well as discusses a future buccal insulin formulation, Oral-Lyn, on the horizon for the treatment of diabetes mellitus.