The Monograph Series is published by NCTM as a supplement to the Journal for Research in Mathematics Education (JRME). Each monograph has a single theme related to the learning or teaching of mathematics. Funded by the National Science Foundation, the purpose of the LOGO Geometry Project was to develop a research-based grades K-6 geometry curriculum that addressed the deficits of the current curriculum. In addition to introducing the project and its rationale, this monograph details the research, results and implications of the study.