We analyze active tectonics in the northern Island of Luzon, Philippines, using campaign GPS geodetic observations combined with focal mechanism data derived from the Harvard Centroid Moment Tensor (CMT) Catalog. Geodetic and seismological data are used to characterize models of crustal deformation and estimate slip rates along faults in this rapidly deforming plate boundary zone, located between two opposing subduction zones. Geologic, geomorphic and geophysical observations obtained from gravity, seismicity, and geologic maps are integrated with Digital Elevation Models and satellite imagery visualizations to define microplates comprising Luzon. Joint inversions based on observed geodetic and seismic data are used to obtain best-fit models which define plate rotations, fault slip rates, and fault locking parameters. Six elastic microplates were found to comprise Luzon. Plate convergence was found to be absorbed through a combination of eastward subduction along the Manila Trench, westward subduction along the Philippine Trench/East Luzon Trough, and sinistral strike-slip motion along the Philippine Fault, Digdig Fault, and the Northern Cordillera Fault. Deformation in southwestern Luzon was found to be partitioned into ~5-10 mm yr-1 transtensional motion along the complex volcanic area of the Macolod Corridor, and ~5-12 mm yr-1 transpression along the Marikina Fault, which runs through Metropolitan Manila. Estimates reveal that the Manila Trench has very low coupling, while the Philippine Trench is partially coupled. The Northern Cordillera Fault and Digdig Faults are found to be almost fully locked, while the segment of the Philippine Fault that failed during the large 1990 earthquake is estimated to be partially (~60%) coupled. Estimates of fault slip rates, combined with estimates of fault coupling, suggest that the areas of highest seismic strain accumulation include the Philippine Fault and its northern extensions, Digdig Fault and the Northern Cordillera Fault.