This book presents experimental studies on small radiation sources such as subwavelength apertures, photonic crystal lasers, and microdisk lasers in their far- and near-field regimes. For the far-field characterization of highly divergent emissions, a solid angle scanner which is capable of scanning a detector and necessary optics over the surface of a sphere centered at the sources is developed. Polarization-resolved two-dimensional angular distributions are measured with this instrument. For the near-field characterization of subwavelength structures, a near-field scanning optical microscope which scans a fiber probe over the source surface with shear-force distance regulation using dual tuning forks is developed. Spectrally-resolved near- field images are measured with this instrument.