  This review deals with the kinetic and thermodynamic fragility of bulk
metallic glass forming liquids. The experimental methods to determine the
kinetic fragility, relaxation behavior and thermodynamic functions of
undercooled metallic liquids are introduced. Existing data are assessed and
discussed using the Vogel-Fulcher-Tammann equation and in the frameworks of the
Adam-Gibbs as well as the Cohen-Turnbull free volume approach. In contrast to
pure metals and most non glass forming alloys, bulk glass formers are
moderately strong liquids. In general the fragility parameter $D^{*} $
increases with the complexity of the alloy with differences between the alloy
families, e.g. noble-metal based alloys being more fragile than Zr-based
alloys. At least some bulk metallic glass forming liquids, such as Vitreloy 1,
undergo transitions from a fragile state at high temperatures to a strong state
at low temperatures with indications that in Zr-based alloys this behavior is a
common phenomenon.
