The Byzantine Iconoclasm (Eikonomachía) refers to two periods in the history of the Byzantine Empire when the use of religious images or icons was opposed by religious and imperial authorities within the Eastern Church and the temporal imperial hierarchy. The "First Iconoclasm", as it is sometimes called, lasted between about 726 and 787. The "Second Iconoclasm" was between 814 and 842. According to the traditional view, Byzantine Iconoclasm constituted a ban on religious images by Emperor Leo III and continued under his successors. It was accompanied by widespread destruction of images and persecution of supporters of the veneration of images. The Western church remained firmly in support of the use of images throughout the period, and the whole episode widened the growing divergence between the East and Western traditions in what was still a unified church, as well as facilitating the reduction or removal of Byzantine political control over parts of Italy.

Iconoclasm, Greek for "image-breaking", is the deliberate destruction within a culture of the culture's own religious icons and other symbols or monuments, usually for religious or political motives. People who engage in or support iconoclasm are called iconoclasts, a term that has come to be applied figuratively to any person who breaks or disdains established dogmata or conventions. Conversely, people who revere or venerate religious images are derisively called "iconolaters" (εἰκονολάτραι). They are normally known as "iconodules" (εἰκονόδουλοι), or "iconophiles" (εἰκονόφιλοι). These terms were, however, not a part of the Byzantine debate over images. They have been brought into common usage by modern historians (from the seventeenth century) and their application to Byzantium increased considerably in the late twentieth century. The Byzantine term for the debate over religious imagery, "iconomachy" means "struggle over images" or "image struggle".