This MESSENGER Magnetic field data set contains cruise-phase magnetic field vectors in RTN coordinates at time resolutions typically of 0.5 s or 1.0 s and sometimes as fine as 0.05 s. The Mercury Surface, Space Environment, Geochemistry, and Ranging, MESSENGER, mission is designed to study the characteristics and environment of Mercury from orbit. The nominal orbit is planned to have a periapsis of 200 km at 60° N latitude, an apoapsis of 15,193 km, a period of 12 hours, and an inclination of 80°. The periapsis will slowly rise due to solar perturbations to over 400 km at the end of 88 days, one Mercury year, at which point it will be readjusted to a 200 km, 12 hour orbit via a two burn sequence. Data will be collected from orbit for one Earth year, the nominal primary mission was planned to end in March 2012. Specifically, the scientific objectives of the mission are to characterize: * the chemical composition of the surface of Mercury * the geologic history * the nature of the magnetic field * the size and state of the core * the volatile inventory at the poles * the nature of the Hermean exosphere and magnetosphere The MESSENGER mission should also yield: * global composition maps * a 3-D model of the magnetosphere of Mercury * topographic profiles of the northern hemisphere * gravity field to degree and order sixteen * altitude profiles of elemental species * a characterization of the volatiles in permanently shadowed craters at the poles The MESSENGER spacecraft is a squat box (1.27 m ⨯ 1.42 m ⨯ 1.85 m) with a semi-cylindrical thermal shade, roughly 2.5 m tall and 2 m wide, for protection from the Sun and two solar panel wings extending radially about 6 m from tip to tip. Five science instruments are mounted externally on the bottom deck of the main body: the Mercury Dual Imaging System, MDIS, Gamma-Ray and Neutron Spectrometer, GRNS, X-ray Spectrometer, XRS, Mercury Laser Altimeter, MLA, and Atmospheric and Surface Composition Spectrometer, MASCS. Radio Science, RS, experiments will use the existing communications system. The Energetic Particle and Plasma Spectrometer, EPPS, is mounted on the side and top deck, and the magnetometer, MAG, is at the end of the 3.6 m boom. The Messenger MAG instrument is a miniature three-axis ring-core fluxgate magnetometer with low-noise electronics. It is mounted on a 3.6 m boom in the anti-sunward direction. The MAG has ±1530 and ±51300 nT ranges with 20-bit internal resolution and 17-bit output resolution. The MAG probe samples magnetic field values along the X, Y, and Z axes at a rate of up to 20 samples/s. The rate is commandable and can vary. This data set has 3-axis calibrated samples of the magnetic field in heliospheric RTN coordinates, Br, Bt, Bn, in units of nT. The spacecraft position data in these files are identified by radial distance from the Sun, latitude above the ecliptic plane, and azimuth with respect to the Earth-Sun line in the ecliptic plane. The MESSENGER Magnetometer data are also available from the Planetary Data System, Planetary Plasma Interactions, PDS/PPI, node via the URL; https://pds-ppi.igpp.ucla.edu/search/view/?f=yes&id=pds://PPI/MESS-E_V_H_SW-MAG-3-CDR-CALIBRATED-V1.0/DATA/RTN/. Hovever, the data are listed in plain text, space delimeted ASCII tables. Note that this SPASE Numerical Description only describes the MESSENGER Magnetometer data stored in Common Data Files.