This book intends to be an updated compilation of the most important buccal, gastric, intestinal, pulmonary, nasal, vaginal, ocular, skin and blood-brain barrier in vitro models for predicting the permeability of drugs. Concepts and Models for Drug Permeability Studies focuses on different approaches and comprises of various models. Each model describes the protocol of seeding and conservation, the application for specific drugs, and takes into account the maintenance of physiologic characteristics and functionality of epithelium, from the simplest immortalized cell-based monoculture to the most complex engineered-tissue models. Chapters also discuss the equivalence between in vitro cell and tissue models and in vivo conditions, highlighting how each model may provisionally resemble a different drug absorption route.