The veneration of icons is a central devotional practice of Eastern Orthodox Christianity, and of the Eastern Catholic churches, in which sacred images of Christ, the Virgin Mary, the angels and the saints are honoured with reverence, bowed to, kissed, censed, and set before candles and lamps. Orthodox theology draws a careful and essential distinction: the honour given to icons is veneration, a relative honour that passes to the person the image represents, and never worship, which belongs to God alone. The icon is understood as a window onto the holy, a point of contact through which the worshipper's reverence reaches the one depicted, and the tradition insists that the image itself is not adored but that the honour shown it ascends to its prototype.
The practice was forged in the fierce controversy of the Iconoclast period, when in the eighth and ninth centuries the Byzantine church was riven by those who condemned the images as idolatry and destroyed them, and those who defended them. The defenders, above all John of Damascus and Theodore the Studite, argued that because God had become visible in the incarnation of Christ, taking flesh and entering the material world, he could rightly be depicted, and that the making and honouring of icons affirmed rather than denied the reality of the incarnation. The Second Council of Nicaea in 787 vindicated the icons and defined the distinction between veneration and worship, and the eventual restoration of the images is still celebrated annually in Orthodoxy as the "Triumph of Orthodoxy." Icons thus carry a weight beyond the devotional: their veneration is bound up with the Orthodox understanding of matter, the incarnation, and the sanctification of the created world.