Patient ocular complaints often center around discomfort, foreign body sensation, and/or recent trauma. Determining the cause of the ailment is not always straightforward, and the use of fluorescein can provide valuable information that aids in clinical diagnosis. Many corneal conditions and emergencies can be identified with the aid of fluorescein such as corneal erosion, superficial punctate keratitis, corneal abrasion, foreign bodies, and tracking patterns of foreign bodies. This article and video will demonstrate proper technique to instill fluorescein and examine ocular tissues, as well as some examples of staining defects characteristic of compromised ocular tissues.