In celebration of its 50th anniversary, the NRAO is hosting a science symposium highlighting the most important questions that can be addressed by astronomers. The universe is a unique laboratory yielding historical data on the creation of the universe, the formation of the first stars and galaxies, the production of the elements, the assembly of molecules and the building blocks of life in interstellar space, how and where planets form, and possible changes in fundamental physical constants on cosmological time scales. This laboratory contains black holes, neutron stars, and gravitational radiation for studying extreme gravity and extremely dense matter. It is filled with the mysterious dark energy and dark matter that control the expansion and destiny of the universe, and whose nature is a critical unsolved problem for physics. This symposium will commemorate major contributions to astronomy enabled by NRAO instruments, and it will bring together leading scientists to review recent discoveries and outstanding key issues to guide future radio observations.