The Deep Extragalactic Exploratory Probe (DEEP) is a multiphase research program dedicated to the study of the formation and evolution of galaxies and of large-scale structure in the distant universe. This paper describes the first five-year phase, denoted DEEP1. A series of 10 DEEP1 papers will discuss a range of scientific topics (e.g., the study of photometric and spectral properties of a general distant galaxy survey, the evolution observed in galaxy populations of varied morphologies). The observational basis for these studies is the Groth Survey Strip field, a 127arcmin^2^ region that has been observed with the Hubble Space Telescope (HST) in both broad I-band and V-band optical filters and with the Low Resolution Imaging Spectrograph on the Keck Telescopes. Catalogs of photometric and structural parameters have been constructed for 11,547 galaxies and stars at magnitudes brighter than 29, and spectroscopy has been conducted for a magnitude-color weighted subsample of 818 objects.