My results suggest that in at least some cases, structural changes at the micro-arcsecond scale coincide with Gamma-ray flaring activity. However, the morphology in GMVA images, suggests that the internal structure is very complex with many quasi-stationary features exhibiting flaring events at similar times. An example is shown here in the famous blazar BL Lac. These complex structures make the conclusive identification of the location of the Gamma-ray flaring difficult. The spectral decomposition of the blazars shows that the magnetic field strengths within the blazar are ~1 Gauss, which in turn suggests that the magnetic field strength near the base of the jet is of the order of thousands of Gauss.