This document describes a data base containing daily observations of maximum and minimum temperature and precipitation amounts from 138 US stations. These stations are a specially chosen subset of the 1219-station US Historical Climatology Network (HCN), compiled by the National Climatic Data Center (Asheville, North Carolina). The daily data network (herein referred to as the HCN/D) consists of stations considered to be the best of those from the HCN, selected to provide reasonably homogeneous spatial coverage of the contiguous US after considering the temporal homogeneity of each station's observing times, instrument types/positions, and surroundings. The data for each station extend through 1987, and most station records are complete for at least 80 years. The daily resolution of these data lends maximum flexibility for studies attempting to detect and monitor long-term climatic changes on a regional scale. Studies using daily data may be able to detect changes in regional climate that would not be apparent from analysis of the more commonly used monthly temperature and precipitation data. Such studies may include analyses of trends in maximum/minimum temperatures, temperature extremes, daily temperature range, precipitation ''event size'' frequency, and the magnitude and duration of wet and dry periods. Other applications of the data include planning and risk assessment in areas such as agriculture, natural resource exploration, and construction. This document describes how the stations in the HCN/D were selected, defines limitations and restrictions of the data, describes the format and contents of the magnetic tape, and provides reprints of literature pertinent to the collection and application of daily climate data.