  A new paradigm for active galactic jet kinematics has emerged through
detailed investigations of BL Lac objects using very long baseline radio
interferometry. In this new scheme, most, if not all, jet components appear to
remain stationary with respect to the core but show significant non-radial
motions. This paper presents results from our kinematic investigation of the
jets of a statistically complete sample of radio-loud flat-spectrum active
galaxies, focusing on the comparison between the jet kinematic properties of BL
Lacs and flat-spectrum radio-quasars. It is shown that there is a statistically
significant difference between the kinematics of the two AGN classes, with BL
Lacs showing more bent jets, that are wider and show slower movement along the
jet axis, compared to flat-spectrum radio-quasars. This is interpreted as
evidence for helically structured jets.
