This is the third in a series of articles to be published in Optometry in Practice covering general pathological principles for the optometrist and describes the mechanisms of inflammation due to any cause. The primary role of inflammation is to wall off and remove a pathological agent before initiating the processes of healing and repair. Inflammation can be acute, chronic, granulomatous or acute-on-chronic (an acute exacerbation of chronic inflammation). Various inflammatory conditions of the eye and adnexa are described to illustrate these pathological processes.