Among the hot stars there exists an interesting class of stars that show significant Balmer line emission, which is thought to originate in a disk-like structure formed by an outflowing material from the central star. Because the exact mechanisms responsible for the disk formation are poorly understood, observational studies that spatially resolve the circumstellar regions are necessary to advance our understanding of these objects. I will describe how interferometric observations with complementary spectroscopic data are used to constrain the theoretical models of the circumstellar disks. Such tests can in turn be used to determine the physical properties of the disks, investigate rotationally enhanced mass-loss processes, and study the effects of a secondary on a circumprimary disk in Be star binaries. Recent progress as well as future plans will also be presented.