Despite its vital role in advancing live cell imaging (LCI) and unraveling the complex processes that control cellular function, fluorescence microscopy presents challenges for the researcher, including labeling agents that can interfere with normal molecular activities, and limitations on repeat measurements and long-term studies from photobleaching and phototoxicity phenomena. Holotomography microscopy delivers nanoscale, label-free, real-time LCI and can combine this quantitative phase imaging (QPI) with fluorescence for state-of-the-art spatiotemporal resolution as well as high molecular specificity. This article introduces QPI, examines its advantages for LCI, and reviews correlative microscopy studies in cell pathophysiology in combination with fluorescence.