Irwin, K.D. MOIXB3 2014 2014-10 Superconducting detectors have grown in scale and sensitivity, and now can greatly improve both measurements of the cosmic microwave background and x-ray spectroscopy at x-ray light sources. Superconducting x-ray spectrometers provide high spectral resolution along with high photon-collection efficiency at x-ray light sources (more than two orders of magnitude higher than provided by gratings) and simultaneous measurement of the full spectrum in each pixel. They operate by measuring a temperature pulse from the absorption of individual x-rays. The temperature pulse is sensed by a superconducting film and amplified by a superconducting amplifier. The development of multiplexed superconducting amplifiers has enabled the construction of arrays of pixels. Kilopixel x-ray calorimeter arrays are planned for both synchrotron and free-electron-laser beamlines, and technology development is underway to scale to megapixel arrays, which would allow nearly 2*pi solid angle coverage and extremely high count rates. Similarly, the temperature and polarization of the cosmic microwave background (CMB) can be determined by measuring a temperature change induced by cosmic microwave background photons from a millimeter-wave telescope. The BICEP-2 experiment at the South Pole recently reported the most sensitive measurement to date of the polarization of the CMB with superconducting detectors, and the first detection of a curl, or "B-mode" pattern in the polarization of the CMB at degree angular scales. Primordial B-mode polarization is the distinctive signature of gravitational waves from inflation at the energy scale of Grand Unification, but additional non-primordial sources of B-mode polarization also exist, including polarized dust and gravitational lensing. I will describe the role of superconducting detectors in x-ray light source measurements, in the BICEP-2 experiment, and also their use in efforts to further understand B-mode signals in the CMB.