Measuring CMB Polarization from the Stratosphere

Measurements of the polarization of the Cosmic Microwave Background (CMB) are a powerful probe of the composition and evolution of the Universe.  Observing from the stratosphere with balloon-borne telescopes provides access to information at high frequencies and on the largest spatial scales.  In this talk, I will discuss what we can learn about cosmology from CMB polarization in the context of two experiments. SPIDER is a balloon-borne telescope designed to look for a signal from cosmic inflation over the course of two Antarctic flights.  The second of these flights, which concluded in January of this year, also provides a unique dataset to characterize the Galactic foregrounds that must be separated from the CMB. I'll also discuss the upcoming Taurus experiment, which is being designed to measure the E-mode polarization signal from reionization over 70% of the sky from a mid-latitude flight.  With different instrument designs and systematic errors, these balloon-borne telescopes are highly complementary to other ground- and satellite-based CMB experiments.