Resident physicians spend numerous hours every week teaching medical students and fellow residents, and only rarely are they taught how to teach. They can, however, be taught to teach more effectively. Teaching skills improvement initiatives for residents are taking a more prominent place in the educational literature. Limited evidence now suggests that better resident teachers mean better academic performance by learners. A small but important body of research supports selected interventions designed to improve residents' teaching skills, but not all studies have demonstrated significant educational benefits for learners. An increasing number of valid and reliable instruments are available to assess residents' clinical teaching, including objective structured teaching examinations and rating scales. In all specialties, rigorous research in evidence-based teacher training for residents will help prepare academic medical centers to meet the diverse and changing learning needs of today's physicians-in-training.