Extrasolar Giant Planet and Brown Dwarf Models

With the discovery of the companions of 51 Peg, 55 Cnc, $τ$ Boo, $\upsilon$ And, 70 Vir, 47 UMa, and Gl229, evolutionary and spectral models of gas giants and/or brown dwarfs with masses from 0.3 through 60 times that of Jupiter assume a new and central role in the emerging field of extrasolar planetary studies. In this contribution, we describe the structural, spectral, and evolutionary characteristics of such exotic objects, as determined by our recent theoretical calculations. These calculations can be used to establish direct search strategies via SIRTF, ISO, and HST (NICMOS), and via various ground-based adaptive optics and interferometric platforms planned for the near future.