The Byzantine Iconoclasm were 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 Ecumenical Patriarchate and the temporal imperial hierarchy. The First Iconoclasm, as it is sometimes called, occurred between about 726 and 787, while the Second Iconoclasm occurred between 814 and 842. According to the traditional view, Byzantine Iconoclasm was started by a ban on religious images promulgated by the Byzantine Emperor Leo III the Isaurian, and continued under his successors. It was accompanied by widespread destruction of religious images and persecution of supporters of the veneration of images. The Papacy remained firmly in support of the use of religious images throughout the period, and the whole episode widened the growing divergence between the Byzantine and Carolingian traditions in what was still a unified European Church, as well as facilitating the reduction or removal of Byzantine political control over parts of the Italian Peninsula.

Iconoclasm is the social belief in the importance of the destruction of icons and other images or monuments, most frequently for religious or political reasons. People who engage in or support iconoclasm are called iconoclasts, a term that has come to be figuratively applied to any individual who challenges "cherished beliefs or venerated institutions on the grounds that they are erroneous or pernicious."