into hybrid quantum systems containing superconducting qubits. We demonstrate the viability of this hybrid systems approach by controllably immersing a three-dimensional superconducting transmon qubit in superfluid 4He. By measuring spectroscopic and coherence properties we find that the cavity, the qubit, and their coupling are all modified by the presence of the dielectric superfluid, which we analyze within the framework of circuit quantum electrodynamics (cQED). At temperatures relevant to quantum computing experiments, the energy relaxation time of the qubit is not significantly changed by the presence of the superfluid, while the pure dephasing time modestly increases, which we attribute to improved thermalization via the superfluid.