Abstract: Quantum computing represents an enormous challenge with the competing requirements of fast manipulation, long storage, and long distance transport of fragile quantum states. Individually these goals have been realized with nanosecond manipulations (quantum circuits), coherence times measured in seconds (atomic ions/nuclear spins), and entanglement transported over kilometers (linear optics). Yet thus far no system has achieved all of the necessary components simultaneously. Just as classical computers have evolved to make use of magnetic, charge, and optical technologies, perhaps the ultimate realization of a quantum computer will also involve hybrid quantum systems. I will describe how superconducting circuits can be used to manipulate single photons, and how they can act as a universal quantum bus to interface with many other physical systems. This hybrid approach can both improve prospects for quantum information science as well as illuminate new physics of the component systems. As a specific example, I will show how superconducting circuits can be coupled to mesoscopic spin ensembles which might serve as a high fidelity quantum memory and also provide a means to access broadband, low temperature (millikelvin), ultra low power (attowatt) electron spin resonance.