Multi-wavelength light curves of Mrk 421 along the MAGIC-I observation period; full circles mark the fluxes observed when MAGIC-I and Swift/XRT were pointed at the source simultaneously. Upper panel: MAGIC-I VHE light curve above 200 GeV, for the 66 observation nights that passed quality cuts. MAGIC-I detected the source clearly in all nights; the integral flux was below the Crab Unit (C.U.,  ≈ F_{E > 200   GeV} = 2.0  ×  10^-10 photons cm^-2   s^-1, represented here by the dashed horizontal line) only in a few nights. A maximum flux of  ~3.6 C.U. was observed on 2008 March the 30th (MJD = 54 555). Middle-upper panel: soft X-ray (0.2 − 10 keV) count rates measured by Swift/XRT. Middle-lower panel: soft X-ray (2 − 10 keV) count rates measured by RXTE/ASM. Lower panel: Johnson R-band optical light curve from the Tuorla Observatory.