Optical Coherence Tomography (OCT) is a high-resolution imaging technique that generates cross-sectional images of biological tissue using low-coherence interferometry. OCT revolutionized ophthalmic diagnosis after its invention as it offered real-time structural examination of the retina and anterior segment at micrometer resolution. This chapter introduces the fundamental principles of OCT technology, including light-tissue interactions, axial and lateral resolution trade-offs, and the evolution from Time-Domain to Spectral- and Swept-Source OCT systems. Limitations to OCT, in spite of clinical success, are low penetration in scattering tissue, motion and shadowing artifacts, device cost, inter-platform variation, and the need for skilled operators. Additionally, although AI-powered OCT interpretation and handheld devices show promise, their clinical use is ongoing. The future prospects are geared towards addressing these limitations by creating multimodal, functional OCT systems, incorporating machine learning, and expanding their use to systemic disease monitoring. OCT is also advancing as a useful tool not just in ophthalmology but in multidisciplinary fields of medicine and biomedical research.