Observations, theoretical analysis, and interpretation of high-energy astrophysical phenomena are conducted at gamma-ray, X-ray, optical/infrared, and radio frequencies. Astrophysical sources include collapsed objects, galactic binaries (neutron stars, black holes), novae, active galactic nuclei, blazars, gamma-ray bursts and transients, solar flares, terrestrial gamma-ray flashes, and unidentified GeV sources. The program’s objectives are to probe cosmic ray acceleration, extreme radiative processes and environments, and electromagnetic counterparts to multi-messenger sources (high-energy neutrinos and gravitational waves). A significant portion of the research focuses on NRL's principal role in the analysis and scientific interpretation of data from the Fermi Gamma-ray Space Telescope mission, and the group is active in many aspects of Fermi science as members of the Large Area Telescope (LAT) collaboration. The group is also actively involved in future high-energy mission concepts. X-ray, optical/infrared, and multi-band radio continuum studies consist of a variety of projects in data analysis using new and archival data. Those core efforts involve NASA Guest Investigator and archival programs with the Chandra X-ray Observatory, XMM-Newton, Swift, NICER, NuSTAR, Fermi, and various multi-wavelength ground-based facilities for optical/near-infrared spectroscopic and radio interferometer studies.