Pharmaceutical scientists increasingly utilize transporters for drug delivery and targeting. The biological barriers to drug delivery can basically be divided into epithelial, endothelial, elimination, and target cell barriers. Membrane transporters play an important role in drug entrance and exit from the body. In addition, it is possible to utilize transporters for drug delivery, e.g., improving oral absorption via the peptide transporter. Identification, a better understanding of their transport characteristics, and the regulation of the membrane transporters will allow the development of better drug delivery strategies.