This volume, the ninth volume in the Handbook of Research in Middle Level Education, is a compilationof research studies focusing on the use and implementation of common planning time(CPT) in middle level schools. All of the studies were part of the Middle Level EducationResearch SIG's National Middle Grades Research Project (NMGRP) on Common Planning Time,which provides additional evidence about teachers' understandings, experiences, the benefits andbarriers about CPT.Since all researchers participating in the SIG-sponsored project utilized the same datacollection protocols and followed the same protocols, the overall data collection was systematic and is highly reliable. Five researchquestions were generated to guide the development of the data collection protocols. While the authors were encouraged to use their datato address these project-level questions, they were not required to do so. The project consisted of both qualitative and quantitative datacollection. Phase I (qualitative) consisted of observations of CPT meetings and structured interviews with teachers. Phase II (quantitative)was comprised of an online teacher survey. Within the chapters of this volume, a variety of relevant and meaningful research questionsare examined utilizing both qualitative and quantitative methodologies.