  We report on the results of two coordinated multiwavelength campaigns that
focused on the blazar Markarian 421 during its 2006 and 2008 outbursts. These
campaigns obtained UV and X-ray data using the XMM-Newton satellite, while the
gamma-ray data were obtained utilizing three imaging atmospheric Cerenkov
telescopes, the Whipple 10m telescope and VERITAS, both based in Arizona, as
well as the MAGIC telescope, based on La Palma in the Canary Islands. The
coordinated effort between the gamma-ray groups allowed for truly simultaneous
data in UV/X-ray/gamma-ray wavelengths during a significant portion of the
XMM-Newton observations. This simultaneous coverage allowed for a reliable
search for correlations between UV, X-ray and gamma-ray variability over the
course of the observations. Investigations of spectral hysteresis and modeling
of the spectral energy distributions are also presented.
