The EHR Core Research (ECR) program offers this ECR:Core solicitation and invites proposals for fundamental research that contributes to the general, explanatory knowledge that underlies STEM education in one or more of the three broadly conceived Research Areas: Research on STEM Learning and Learning Environments, Research on Broadening Participation in STEM fields, and Research on STEM Workforce Development. The solicitation has three levels of funding with a range of budget sizes, and proposals may request a duration of 3 to 5 years for any level. Key aspects of the opportunity include: • Fundamental research that generates knowledge and understanding with the potential for broad relevance • Proposals that focus on the advancement or refinement of foundational knowledge for STEM education • A range of budget sizes, with Level I proposals requesting up to $500,000, Level II proposals requesting up to $1,500,000, and Level III proposals requesting up to $2,500,000 • A duration of 3 to 5 years for any level of funding • The need for proposals to justify the level of funding and duration in the project description