The Theory group has a broad ranging research program that focuses on understanding all forms of nuclear matter that comprise the visible universe. At the smallest scales, this includes the quark and gluon structure of protons and neutrons, together with other intriguing strongly interacting particles such at the pion and kaon, and expands to include the structure and reactions of atomic nuclei across the chart of nuclides, and at the largest scales we study exotic states of matter such as those found in neutron stars. Our research endeavors to answer profound questions, such as: Why are quarks and gluons confined inside the nucleon? How do quark and gluon dynamics generate the nucleon mass and spin? What is the 3-dimensional confined motion and spatial distribution of quarks and gluons in nucleons and nuclei? What is the best description of the effective forces between nucleons in nuclei?  Why are some nuclei stable, and what are the limits of nuclear stability?  For unstable nuclei, what are the mechanisms by which they decay? How would new physics beyond the Standard Model interact with hadrons and nuclei? In addressing these questions, we place a strong emphasis on the prediction of phenomena accessible at current and future facilities in the United States and worldwide, e.g., the Argonne Tandem Linac Accelerator System (ATLAS), Fermilab, Jefferson Lab, the Facility for Rare Isotope Beams (FRIB), the Relativistic Heavy Ion Collider (RHIC), and the Electron-Ion Collider (EIC). Our research also explores the use of emerging technologies, such as quantum computing and machine-learning techniques.