In the 15 years since the last Institute of Laboratory Animal Resources report on the general management of rodents was published, important advances in biomedical research and increased public awareness have created a new environment for animal research. Modern technology-such as insertion of functional genes from other species into mice or rats, elimination of a single selected gene or function in mice, and the re-creation of elements of the human immune system in mice-has greatly expanded the usefulness of rodents in drug development and as models of human diseases. The technologic requirements of such advanced systems have led to improved understanding and implementation of environmental requirements for the care and use of rodents in research. The intent of this report is to provide current information to laboratory animal scientists (including both animal-care technicians and veterinarians), investigators, research technicians, and administrators on general elements of rodent care and use that should be considered both for optimal design and conduct of research and to meet current standards of care and use.