The Delphi technique has been around for some time now. It is difficult to resist the urge here to recapitulate the story of its
origins, but we will: these details are noted in various papers in this special issue. One moment of history that is worth emphasising,
however, is that of 1975,when the first edition of Linstone and Turoff's [1] edited book on Delphi first appeared and brought notice of
the approach to awider audience. Slowly at first, but at a seemingly growing rate, the technique has flourished, appearing inmore and
more academic domains and being used for more andmore purposes. As evidence of the impact of that work, Google Scholar reveals
that ‘The Delphi Method: Techniques and Applications’ has been cited over 2700 times (while it has undoubtedly been mis-cited
many more times too). Furthermore, as Delphi's ubiquity has grown, so has themethod evolved, with the development of numerous
variants, so that it is perhaps better to talk of ‘Delphi techniques’ in the plural than in the singular. As such, though not quite at the
50th anniversary of publication of that seminal Delphi volume, now seems an apt moment to consider exactly how the method
has developed, into what new areas and forms, and to what ends (especially since such a review/compendium has not occurred in
this journal since one in 1975). Such consideration is the aim of this special issue