The purpose of this funding opportunity announcement (FOA) is to invite applications for multisite clinical trials and observational studies developed in conjunction with NICHD Networks that will be conducted using NICHD-supported Network infrastructure. The goal of this FOA is to operationalize the previously reported NICHD guiding principles for multisite clinical trials delineated in Notice NOT-HD-19-034:To enhance the rigor and reproducibility of clinical trial protocolsTo promote greater availability of multisite clinical trial infrastructure to support trials from a wider range of investigatorsTo facilitate data sharing and access to biospecimens to efficiently expand research capacity for all investigatorsTo facilitate greater involvement of diverse populations in multisite clinical trials.Consequently, multisite clinical trials and observational studies conducted by and within the participating NICHD-supported Clinical Research Networks will be submitted as investigator-initiated, multi-Principal Investigator (PI) grant applications by any qualified investigator in the extramural community (including NICHD Network investigators) in conjunction with the respective NICHD Network Data Coordinating Center (DCC). It is the intent of this initiative to utilize the NICHD Clinical Research Network infrastructure in a manner that will promote the funding and support of the best science in a timely, transparent, equitable and cost-effective manner.