With a peak absolute V-band magnitude brighter than −20.5, a peak bolometric luminosity of 1.7×10^44 ergs s−1, and a total radiated energy of 2.1×10^50 ergs, ASASSN-14ms is one of the most luminous Type Ibn supernovae yet discovered. We present photometric and spectroscopic follow-up observations of this event, and examine a number of simple models. We find that the most likely power source is a combination of the radioactive decay of Ni and Co at late times and the interaction of supernova ejecta with the progenitor's circumstellar medium at early times, although we cannot rule out the possibility of a magnetar-powered light curve.