  In this paper, we review spatial light interference microscopy (SLIM), a
common-path, phase-shifting interferometer, built onto a phase-contrast
microscope, with white-light illumination. As one of the most sensitive
quantitative phase imaging (QPI) methods, SLIM allows for speckle-free phase
reconstruction with sub-nanometer path-length stability. We first review image
formation in QPI, scattering, holography, and microcopy. Then, we outline SLIM
imaging from theory to instrumentation. Zernike phase-contrast microscopy,
phase retrieval in SLIM, and halo removal algorithms are discussed. Next, we
discuss the requirements for operation, with a focus on software developed
in-house for SLIM that high-throughput acquisition, whole slide scanning,
mosaic tile registration, and imaging with a color camera. Lastly, we review
the applications of SLIM in basic science and clinical studies. SLIM can study
cell dynamics, cell growth and proliferation, cell migration, and mass
transport, etc. In clinical settings, SLIM can assist with cancer studies,
reproductive technology, and blood testing, etc. Finally, we review an emerging
trend, where SLIM imaging in conjunction with artificial intelligence (AI)
brings computational specificity and, in turn, offers new solutions to
outstanding challenges in cell biology and pathology.
