A ‘red eye’ is a common complaint with which patients present to the urgent eye care service. Many eye conditions can cause a red eye, including infections, inflammation and trauma. This chapter highlights the importance of identifying risk factors, when to perform investigations and directs treatment options depending on likely causes. It is up to the casualty officer to come up with a list of differential diagnosis using the method given, to treat the cause of the red eye effectively, whilst avoiding the common pitfalls.