The first use of the term evocation was for the religious/magical practice of calling the tutelary deities of a city out of it so attackers could succeed in their conquest. The deity in question was promised worship by the attackers in the future.
The calling forth of spirits was a relatively common practice in Neoplatonism, theurgy and other esoteric systems of antiquity. In contemporary western esotericism, the magic of the grimoires is frequently seen as the classical example of this idea. Manuals such as the Greater Key of Solomon the King, The Lesser Key of Solomon (or Lemegeton), the Sacred Magic of Abramelin the Mage and many others provided instructions that combined intense devotion to the divine with the summoning of a personal cadre of spiritual advisers and familiars.
The grimoires provided a variety of methods of evocation. The Spirits are, in every case, commanded in the name of God - most commonly using cabalistic and Hellenic 'barbarous names' added together to form long litanies. The magician used wands, staves, incense and fire, daggers and complex diagrams drawn on parchment or upon the ground. In Enochian magic, spirits are evoked into a crystal ball or mirror, in which a human volunteer (a 'seer') is expected to be able to see the spirit and hear its voice, passing the words on to the evoker. Sometimes such a seer might be an actual medium, speaking as the spirit, not just for it. In other cases the spirit might be 'housed' in a symbolic image, or conjuring into a diagram from which it cannot escape without the magician's permission.
While many later, corrupt and commercialised grimoires include elements of 'diabolism' and one (The Grand Grimoire) even offers a method for making a pact with the devil, in general the art of evocation of spirits is said to be done entirely under the power of the divine. The magician is thought to gain authority among the spirits only by purity, worship and personal devotion and study.
In more recent usage, evocation refers to the calling out of lesser spirits (beneath the deific or archangelic level), sometimes conceived of as arising from the self. This sort of evocation is contrasted with invocation, in which spiritual powers are called into the self from a divine source.
Important contributors to the concept of evocation include Henry Cornelius Agrippa, Francis Barrett, Samuel Liddell MacGregor Mathers, Aleister Crowley, Franz Bardon and Kenneth Grant. The work of all of these authors can be seen as attempts to systematize and modernize the grimoiric procedure of evocation. Only more modern authors, such as Peter Carroll, have attempted to describe evocation in a way independent enough from the grimoiric tradition to fit similar methods of interaction with alleged supernatural agents in other traditions.
Religions that use this type of ritual are often judged and criticized by monotheists as potentially Satanic. However, this is not true from the viewpoint of study of religion. Evocation is a practice held sacred by societies such as the American Indian Tribes, most ancient religions and even the Jews in biblical times. This rite is not a "secret" in the society. It is common, practiced openly and frequently not distinguishable from prayer.