The spinor representation is developed and used to investigate minimal
surfaces in {\bfR}^3 with embedded planar ends. The moduli spaces of
planar-ended minimal spheres and real projective planes are determined, and new
families of minimal tori and Klein bottles are given. These surfaces compactify
in S3 to yield surfaces critical for the M\"obius invariant squared mean
curvature functional W. On the other hand, all W-critical spheres and
real projective planes arise this way. Thus we determine at the same time the
moduli spaces of W-critical spheres and real projective planes via the
spinor representation.Comment: 63 pages, dvi file only, earlier version is GANG preprint III.27
available via http://www.gang.umass.edu