In large numbers of elementary and secondary schools across the United States teachers are being called upon to provide support to colleagues through a process called "instructional coaching." Despite widespread implementation of this role, resulting in part from federal initiatives, there is little consensus regarding its operational definition and little empirical research related to it. Following a brief description of the evolution of coaching along with a descriptive discussion of its implementation in schools, the authors describe various implementations of coaching, concluding that there is a need for fully-articulated theoretical and operational models of instructional coaching. The authors compare various coaching approaches to instructional and collaborative consultation and suggest that there is good reason for active communication and collaboration between consultants and coaches operating within the same schools. Finally, they describe current trends and needs related to professional development of instructional coaches and articulate a research agenda related to the field. (Contains 1 table.)