The field of organic thin films and devices is progressing at an extremely rapid pace. Organic-metal and organic-organic interfaces play crucial roles in charge injection into, and transport through, these devices. Their electronic structure, chemical properties, and electrical behavior must be fully characterized and understood if the engineering and control of organic devices are to reach the levels obtained for inorganic semiconductor devices. This article provides an extensive, although admittedly nonexhaustive, review of experimental work done in our group on the electronic structure and electrical properties of interfaces between films of pi-conjugated molecular films and metals. It introduces several mechanisms currently believed to affect the formation of metal-organic interface barriers. (C) 2003 Wiley Periodicals, Inc.