Optical coherence tomography (OCT) is an optical ranging technique analogous to radar - detection of back-scattered light produces a signal that is temporally localized at times-of-flight corresponding to the location of scatterers in the object. However the interferometric collection technique used in OCT allows, in principle, the coherent collection of data, i.e. amplitude and phase information can be extracted. Interferometric Synthetic Aperture Microscopy (ISAM) adds phase-stable data collection to OCT instrumentation and employs physics-based processing analogous to that used in Synthetic Aperture Radar (SAR). That is, the complex nature of the coherent data is exploited to give gains in image quality. Specifically, diffraction-limited resolution is achieved throughout the sample, not just within focal volume of the illuminating field. Simulated and experimental verifications of this effect are presented. ISAM's computational focusing obviates the trade-off between lateral resolution and depth-of-focus seen in traditional OCT.