This article is the first in a two-part series describing the operation, characteristics, and application of a new class of solid-state multichannel UV-visible detectors. In this paper, charge transfer devices (CTDs) are described. Detector characteristics pertinent to spectroscopic application—including quantum efficiency, read noise, dark count rate, and available formats—are emphasized. Unique capabilities, such as the ability to nondestructively read out the detector array and the ability to alter the effective detector element size by a process called binning, are described. CTDs with peak quantum efficiencies over 80% and significant responsivity over the wavelength range of 0.1 nm to 1100 nm are discussed. Exceptionally low dark count rates, which allow integration times of up to many hours and read noises more than two orders of magnitude lower than those read by commercially available PDA detectors, contribute to the outstanding performance offered by these detectors.