Advances in biotechnology have produced therapeutically active proteins on a commercial scale, and therapeutic proteins are now extensively applied in medical practices to treat various diseases. Oral delivery of protein drugs is a highly attractive approach, and, naturally, numerous attempts have been made to develop such formulations. Despite various attempts, however, no clinically useful oral formulations have been developed, and this is mainly due to extremely low bioavailability of protein drugs. The effective oral protein delivery needs to overcome barriers related to poor absorption, poor permeation, and degradation in the gastrointestinal tract. Various strategies have been explored for enhancing the bioavailability of orally administered proteins. They include chemical modification of protein drugs, use of enzyme inhibitors, and exploration of special formulation ingredients, such as absorption enhancers and mucoadhesive polymers. This article examines the current technologies under development for oral protein delivery. (C) 2010 Elsevier Ltd. All rights reserved.