Inter-W Bose-Einstein correlations...or not?

A critical summary is given of the present status of the study of Bose-Einstein correlations in W-pair production at LEP II. In particular, the evidence is reviewed for or against the existence of Bose-Einstein correlations between pions originating both from a different of the two W's. If present, such an inter-W interference would not only form a potential bias in the determination of the W mass, but also would provide a laboratory to measure the space-time development of the overlap. If absent, this would drastically change the conventional (Hanbury Brown and Twiss) picture of pion interferometry in high energy physics. (10 refs).