The National Institute for Occupational Safety and Health (NIOSH) supports exploratory and developmental research projects (R21) that address issues related to diagnostic or treatment uncertainty with respect to individuals receiving monitoring and/or treatment under subtitle C of the James Zadroga 9/11 Health and Compensation Act of 2010.The Zadroga Act lists the following broad research areas:Physical and mental health conditions that may be related to the September 11, 2001, terrorist attacks;Diagnosing WTC-related health conditions for which there has been diagnostic uncertainty; andTreating WTC-related health conditions for which there has been treatment uncertainty.The WTC Health Program intends to increase opportunities for research on new, innovative approaches, interventions, techniques, or methodologies to improve treatment and diagnostic effectiveness through intervention, as well as support program evaluation.The WTC Health Program seeks to achieve a suitable mix of meritorious research projects which assess the feasibility of enhancing interventions and program evaluations to improve diagnosis, treatment, care, and well-being of 9/11-exposed populations.Research areas of interest include clinical, screening, diagnostic, epidemiological, treatment, prevention, translation, and program evaluation. WTC responders, screening-eligible WTC survivors, and certified-eligible WTC survivors comprise the population targeted for the research project.The research should consider health equity initiatives in design, where possible. Opportunities for future health effects research involving vulnerable groups of persons (e.g., minorities, women, children, and other potentially disadvantaged groups) who were exposed to the 9/11 attacks and aftermath are of special interest. Research is needed to identify at-risk groups, characterize the health burden, and inform care.This WTC Health Program R21 Notice of Funding Opportunity (NOFO) is intended to encourage exploratory/developmental research by providing support for the early and conceptual stages of project development which assess the feasibility of new areas of investigation with the potential to enhance treatment effectiveness and diagnostic practices. These studies may lead to breakthroughs in a particular area, or to the development of new interventions, techniques, agents, methodologies, models, or approaches with major clinical impacts. These studies are expected to break new ground or extend prior discoveries toward new directions or uses. Applicants are expected to propose research for which there is likely to be minimal or no preliminary data.The WTC Health Program Research webpage provides comprehensive information and tools for researchers. The research agenda, publication library, and other resources, including the Funding Dashboard, can also be found there (e.g., awarded project details such as publications, topics, populations, funding awarded, and the principal investigators and their institutions).