We propose to obtain snapshot images of a large, well defined, and dynamically selected sample of close galaxy pairs at moderate redshift. These pairs have been selected from the CNOC2 Field Galaxy Redshift Survey (0.1 < z < 0.55), the largest such sample available. This pair sample, in combination with a large low-z sample (SSRS2; z<0.1), is being used for a detailed study of galaxy mergers and interactions over the range z=0-0.5. At low redshift, we have established that the majority of SSRS2 pairs satisfying our criteria (projected separation < 20 h^-1 kpc and line-of-sight velocity difference < 500 km/s) are undergoing interactions. We have developed an improved approach to pair statistics that allows us to trace the evolution in the galaxy merger rate with redshift. We intend to use WFPC2 I-band images to identify morphological signs of interactions in 72 moderate-z pairs, thereby determining whether these pairs really are analogous to their local counterparts. In addition, we will investigate how the rate of interactions/mergers is changing with redshift. Finally, these images will allow us to identify a pure sample of interacting galaxies, permitting a detailed analysis of their properties and a direct comparison with field galaxies. This study will provide a much needed link between detailed studies of nearby pairs (e.g., the Antennae) and those at high-z, and it will elucidate the significance of mergers and interactions in the evolution of galaxies.