  We apply a two-zone MHD model to the jet of M87. The model consists of an
inner relativistic outflow, which is surrounded by a non-relativistic outer
disk-wind. The outer disk-wind collimates very well through magnetic
self-collimation and confines the inner relativistic jet into a narrow region
around the rotation axis. Further, we show by example, that such models
reproduce very accurately the observed opening angle of the M87 jet over a
large range from the kiloparsec scale down to the sub-parsec scale.
