Rapid Variability: What do we learn from correlated mm-/gamma-ray
  variability in jets ?
  Densely time sampled multi-frequency flux measurements of the extreme BL Lac
object S5 0716+714 over the past three years allow us to study its broad-band
variability, and the detailed underlying physics, with emphasis on the location
and size of the emitting regions and the evolution with time. We study the
characteristics of some prominent mm-/gamma-ray flares in the context of the
shock-in-jet model and investigate the location of the high energy emission
region. The rapid rise and decay of the radio flares is in agreement with the
formation of a shock and its evolution, if a geometrical variation is included
in addition to intrinsic variations of the source. We find evidence for a
correlation between flux variations at gamma-ray and radio frequencies. A two
month time-delay between gamma-ray and radio flares indicates a non-cospatial
origin of gamma-rays and radio flux variations in S5 0716+714.
