TRB Transportation Research Circular E-C106: Environmental Geospatial Information for Transportation summarizes a May 3-4, 2006, peer exchange that took place in Washington, D.C. The peer exchange highlighted several examples of successful collaboration, data sharing, and the effective use of environmental geospatial information systems data in transportation planning. The report focuses on environmental stewardship, streamlining, and sustainable growth; the importance of effective collaboration; and building capacity for data management and sharing. Appendices to the report include the final meeting agenda, biographies of presenters and panelists, contact information for all participants, descriptions of applications showcased by participants, responses of Mid-Atlantic states to a preconference questionnaire, and references for related initiatives and resources.