Since Biopharmaceutics operates at the interface of pharmaceutics & physiology, we open with a brief review of the anatomy and physiology of the GI tract for common species. This talk highlights the observations and studies that emphasize the similarities and differences in species and routes of administration. From transdermal to oral, examples of formulations for veterinary practice are presented which emphasize a different clinical or pharmacokinetic outcome between species. Included in the case studies are explanations for this difference. We will see that this difference can be predicted (and sometimes eliminated) once we understand the species-specific physiology, and pharmaceutics of the formulation, ie Biopharmaceutics.