This review article discusses the use of corneal epithelial thickness mapping (ETM) in assessing corneal health and disease. ETM, which provides a detailed map of the corneal epithelium (CE) thickness, is generated using technologies such as very high-frequency ultrasound (VHF-US) and spectral-domain optical coherence tomography (SD-OCT). The review covers normal corneal epithelium, corneal diseases like keratoconus (KCN), corneal dystrophies, limbal stem cell deficiency, and other conditions, as well as the role of ETM in refractive surgery planning and postoperative evaluation. ETM is valuable for detecting subtle changes in the corneal epithelium that may not be visible with conventional methods. It helps in differentiating between normal and abnormal corneal structures, identifying early signs of disease, and monitoring the effectiveness of treatments such as collagen cross-linking (CXL). The review also discusses the variability of CET across different populations, including gender, age, and ocular biometric parameters, and the impact of factors such as intraocular pressure, diurnal changes, and contact lens wear on ETM. The study highlights the importance of ETM in diagnosing and managing corneal diseases, particularly KCN, where ETM patterns can indicate the presence and severity of the condition. It also discusses the use of ETM in refractive surgery, where it aids in preoperative assessment, surgical planning, and postoperative evaluation. The review emphasizes the need for standardized ETM protocols and the importance of considering various factors that may influence ETM results. Overall, ETM is a powerful tool for understanding corneal health and disease, providing detailed insights that are crucial for clinical decision-making.This review article discusses the use of corneal epithelial thickness mapping (ETM) in assessing corneal health and disease. ETM, which provides a detailed map of the corneal epithelium (CE) thickness, is generated using technologies such as very high-frequency ultrasound (VHF-US) and spectral-domain optical coherence tomography (SD-OCT). The review covers normal corneal epithelium, corneal diseases like keratoconus (KCN), corneal dystrophies, limbal stem cell deficiency, and other conditions, as well as the role of ETM in refractive surgery planning and postoperative evaluation. ETM is valuable for detecting subtle changes in the corneal epithelium that may not be visible with conventional methods. It helps in differentiating between normal and abnormal corneal structures, identifying early signs of disease, and monitoring the effectiveness of treatments such as collagen cross-linking (CXL). The review also discusses the variability of CET across different populations, including gender, age, and ocular biometric parameters, and the impact of factors such as intraocular pressure, diurnal changes, and contact lens wear on ETM. The study highlights the importance of ETM in diagnosing and managing corneal diseases, particularly KCN, where ETM patterns can indicate the presence and severity of the condition. It also discusses the use of ETM in refractive surgery, where it aids in preoperative assessment, surgical planning, and postoperative evaluation. The review emphasizes the need for standardized ETM protocols and the importance of considering various factors that may influence ETM results. Overall, ETM is a powerful tool for understanding corneal health and disease, providing detailed insights that are crucial for clinical decision-making.