The GRACE gravity group at GSFC pioneered the estimation of global mass concentration blocks (mascons) from the GRACE Level-1B satellite-to-satellite K-band range-rate (KBRR) measurements. These unique solutions apply prior knowledge of the geophysical signals via constraints towards improved solutions and the reduction of signal leakage across constraint region boundaries. The monthly mascon solutions now span more than a decade, and provide critical information of global water mass variability for hydrologic, cryospheric, and oceanographic research.