αS: from DIS to LEP ∗

The strong coupling αS is a fundamental parameter of the Standard Model. In comparison to parameters like αem, MZ and sin 2 θW it is relatively poorly known. However the precision of αS measurements has improved dramatically in recent years. More than twenty different types of process, from lattice QCD studies to the highest energy colliders, can be used to measure αS accurately. The most precise determinations now quote uncertainties in αS(M 2 Z) of less than 5%. There is also a remarkable consistency between the various measurements. A comprehensive review of αS measurements, including detailed descriptions of the underlying physics for the most important processes, can be found in Ref. [1]. One year later, several of the measurements quoted in Ref. [1] have been updated, resulting in a slight shift in the overall ‘world average’ value. The purpose of the present review is to update the discussion on αS measurements given in Ref. [1], focusing on the new values reported in the last year. For more theoretical details, descriptions of other measurements and a full set of references, the reader is referred to the original review in Ref. [1]. The current situation is summarised in Fig. 1, which updates Table 12.1 of Ref. [1]. Before discussing the new measurements in detail, we begin with some