Composer John Williams, fresh from the Wagnerian success of Star Wars, was allowed the unusual luxury of composing much of the Close Encounters score before principal photography began. Thus Spielberg was able (as had Sergio Leone with Morricone's Once Upon a Time in the West) to stage much of his action to the Williams music playing on the set in a rare way. The entire special-effects finale was in fact edited to match the composer's rhythms.
For his part, Williams composed arguably his most ambitious and accomplished score. Balancing his more obvious sentimental skills with refreshingly bracing doses of atonality (and just a nod to the modern Ligetti pieces Stanley Kubrick had wedded so well to 2001: A Space Odyssey). Williams produced a mature work that holds up remarkably well 20 years on; a true classic. --Jerry McCulley