This report's STEM Workforce Development & Afterschool Learning research agenda is intended to inform researchers of critical questions and appropriate strategies to further describe STEM career exploration and pathways experiences in out-of-school time. The overarching goal of the agenda is to identify and provide an evidence base for promising, replicable practices that ultimately strengthen and diversify the STEM workforce. The agenda was co-developed by participants in the June 2010 National Science Foundation ITEST Convening: Defining an Afterschool Research Agenda. The 2010 Convening included researchers in STEM and informal learning, afterschool leaders and practitioners, and policymakers, funders, and industry professionals. All expressed a commitment to crafting and advancing a collaborative research agenda, through the 2010 gathering and beyond.