This experiment, CELIAS (Charge, Element, and Isotope Analysis System), is designed to study the composition of the solar wind and of solar and interplanetary accelerated energetic particles. It consists of three different particle sensors, each optimized to one of these aspects, plus a fourth sensor to monitor the absolute EUV flux from the sun. The sensors are: Charge Time Of Flight (CTOF), solar wind Mass TOF (MTOF), Suprathermal TOF (STOF), and Solar Extreme-ultraviolet Monitor (SEM). The CELIAS particle energy ranges are designed to complement those of the COSTEP and ERNE experiments also on SOHO. The TOF sensors employ electrostatic deflection systems combined with TOF measurements. The CTOF covers the energy per charge range 0.1--55 KeV/charge, and will determine the composition, charge state distribution, kinetic temperature and speed of the more abundant solar wind ions (e.g., He, C, N, O, Ne, Mg, Si, and Fe). The field of view is a cone of 50 degrees. MTOF is a high-resolution retarding potential mass analyzer with a quadrapole electric field configuration, for measuring the composition of the less abundant elements in the solar wind, and also the isotopic composition of the more abundant heavy ions. The ions within the passband of the electrostatic section pass through a thin carbon foil, where they are scattered and emerge either as neutrals or singly-ionized. Secondary electrons emitted from the foil will generate the start signal, while the ions will generate the stop signal. The STOF is an ion telescope with 0.1 sq cm sr geometric factor. It covers 20--3000 KeV/charge with the electrostatic deflection system, and uses a TOF analysis similar to that of MTOF, plus a final energy measurement in a solid state detector. The SEM consists of a 5000 lines/mm gold transmission grating in front of a set of three absolutely calibrated silicon light diodes, which are covered with an aluminum filter (total thickness 150 nm). The diodes are placed at the zero- and first-order diffraction image of the sun to isolate the 30.4 nm He II line. Due to the extended source of the sun (0.5 degrees) and the 2 mm x 10 mm entrance slit, the spectrometer bandwidth is +/- 4.0 nm. There is a digital processing unit that serves all sensors. It receives, compresses, stores, and formats data for input into the spacecraft telemetry. This information is from the paper ``The Charge, Element, and Isotope Analysis System CELIAS on SOHO,'' by D. Hovestadt (Proceedings of the First SOHO Workshop, ESA SP-348, pp. 39-42, November 1992).