Essays commemorating Arthur Koestler's seventieth birthday and a body of work that would seem to call for a panel of Rand Institute specialists. Koestler's a figure who makes normal people in their conventional groupings rather uncomfortable, not only by reaching as far as he does--from politics to the paranormal and, in between, to the heights represented by The Act of Creation--but also by his consistently provocative stances: his political and scientific ""apostasies,"" the hubris of his comprehensive theory of hierarchies (Roy Webbedy's overview sets matters right by identifying it not as a novelist's imaginative folly, but as an early, underappreciated contribution to systems theory). And then there is Koestler's embarrassing refusal to waive the subject of freedom. It's hard to imagine festivities arising around his somewhat cantankerous personality but that is in fact the mood as contributors from a number of fields, many apparently friends, explicate, assess, sometimes tease Friar's-Club fashion. Mark Graubard defends The Sleepwalkers; Frank Barron applies psychometric validation; T. R. Fyvel compares Koestler and Orwell; Rene Haynes reviews the farther-out researches; Paul D. MacLean gives a playful twist to Koestler's model of the mind; Cynthia Koestler remembers. . . they all write beautifully, and the content is spirited. Happy birthday!