A Rydberg atom consists of a loosely bound electron circling an ion core. Rydberg atoms are remarkable for their exaggerated properties, including large size, extreme sensitivity to electric fields and long decay lifetimes. They have been extensively studied since the invention of the dye laser in the 1970's. Our group in Waterloo concentrates on the interactions between translationally cold Rydberg atoms, obtained by excitation of laser cooled gases. One novel aspect of this work is the precise determination of atomic energy levels without radiative fields. In this talk I will discuss the general properties of Rydberg atoms, our recent results on the interactions between very cold Rydberg atoms, and an ongoing experiment that will use Rydberg atoms as probes of small electric fields above metallic surfaces.