NOAA's National Geophysical Data Center (NGDC) has extensive holdings of airborne and marine magnetic data. Such data have been collected for more than half a century, providing global coverage of the Earth. Due to the changing main field from the Earth's core, and due to differences in quality and coverage, combining these data to a consistent global magnetic anomaly grid is challenging. A key ingredient is the long wavelength magnetic field observed by the low-orbiting CHAMP satellite. To produce a homogeneous grid, the marine and aeromagnetic trackline data are first line-leveled and then merged with the existing grids of continental-scale compilations by Least Squares Collocation. In the final processing step the short-to-intermediate wavelengths of the near-surface grid are merged with a CHAMP satellite magnetic anomaly model. In analogy to NGDC's 2-arcminute resolution ETOPO2 grid, we call our initial 3-arcminute magnetic anomaly grid EMAG3. The grid will be updated regularly. It is available in digital form and as plug-ins for NASA World Wind and Google Earth.