Light curves of Mrk 421 from radio to VHE from 2009 January 19 (MJD 54 850) to 2009 June 1st (MJD 54 983). Vertical bars denote flux measurement errors, and the horizontal bars denote the time bin widths into which some of the light curves are binned. The Fermi-LAT photon fluxes are integrated over a three-day-long time interval. The Whipple 10-m data (with an energy threshold of 400 GeV) were converted into fluxes above 300 GeV using a power-law spectrum with index of 2.5.