*Note: This data has been reprocessed by NCEI adding quality flags and using consistent file formats across the period of record (POR). It is highly recommended that users access this version of the data. The Space Environment Monitor (SEM) is a suite of instruments onboard the GOES satellite series. The objective of the SEM package is to measure solar radiation in the X-ray and Extreme Ultraviolet (EUV) region, the in-situ magnetic field, and the energetic particle environment at geosynchronous orbit. This collection (v1) contains L1B and L2 data from GOES 1-15 and SMS 1-2. The SEM suite on SMS 1-2 and GOES 1-5 is composed of three sensors: SEM/EPS (Energetic Particle Sensor), SEM/MAG (Magnetometer) , and SEM/XRS (X-Ray Sensor). The SEM/HEPAD (High Energy Proton and Alpha Particles Detector) began with GOES 7. The GOES 13-15 SEM suite added these 3 sensors: SEM/EUVS (Extreme Ultraviolet Sensor), SEM/MAGED (Magnetospheric Electron Detector), and SEM/MAGPD (Magnetospheric Proton Detector). On GOES 13-15, the historical EPS sensor was renamed EPEAD (Electron, Proton, and Alpha Detector) and the term EPS now refers to the suite of particle detectors (EPEAD, MAGED, MAGPD). Combined these sensors provide magnetic field, energetic particle, and solar x-ray and EUV data. The magnetometer (MAG) measures the magnitude and direction of the magnetic field. The energetic particle detectors (EPS, HEPAD, EPEAD, MAGED, MAGPD, and MAGED) measure a spectrum of electron, proton, and alpha-particle fluxes caused by solar activity and galactic cosmic rays. The solar x-ray sensor (XRS) measures solar X-ray fluxes for the wavelength bands of 0.05-.4 nm (short channel) and .1 to .8 nm (long channel). The extreme ultraviolet sensor (EUVS) measures the EUV in 5 bands (A-E) spanning wavelengths 5-127 nm. The temporal period of record (POR) for this collection extends from July 1974 to March 2020. The L1b products include full-resolution data (cadence varies by sensor/satellite) provided in daily files in netcdf and csv formats. The L2 products include monthly averages (1 minute or 5 minute cadence) provided in monthly files in netcdf and csv formats. The data were produced by NOAA’s National Centers for Environment Information (NCEI) and archived by NOAA's Comprehensive Large Array-Data Stewardship System (CLASS).