Astronomy is at times a science of unexpected discovery. When it is, and if we are lucky, new intellectual territories emerge to challenge our views of the cosmos. The recent indirect detections using high-precision Doppler spectroscopy of more than one hundred giant planets orbiting more than one hundred nearby stars is an example of such rare serendipity. In this talk, I will survey the physics, chemistry, and astrophysics of extrasolar giant planets (EGPs), focusing on their structures, evolution, compositions, spectra, radii, and transits. In the process, I will demonstrate the numerous familial links between EGPs and the substellar brown dwarfs now being discovered in profusion in the solar neighborhood and in young stellar clusters. However, and importantly, to determine an extrasolar giant planet's physical character requires the direct detection of its light, either in reflection or by thermal emission. Therefore, I will conclude my talk by addressing the maturing physical theory of irradiated EGPs, their spectral signatures, and light curves and put this theory in the context of the numerous proposed astronomical campaigns of extrasolar planet discovery and remote sensing.