The Wide-field Infrared Survey Explorer (WISE), launched in December 2009, is a NASA-funded Explorer mission that
is providing an all-sky survey in the mid-infrared with far greater sensitivity and resolution than any previous IR survey
mission. The Utah State University Space Dynamics Laboratory designed, fabricated, and characterized the science
payload, which is a cryogenically cooled infrared telescope with four 1024x1024 infrared focal plane arrays covering
from 2.8 to 26 μm. Pre-launch characterization included measuring focus, image quality, repeatability, response nonlinearity,
saturation, latency, absolute response, flatfield, point response function, scanner linearity, and relative spectral
response. This paper provides a brief overview of the payload, discusses pre-launch characterization methods, and
presents key performance results from ground characterization and early on-orbit performance.