As described by Snorri Sturlusson in his Ynglinga saga (sec. 7), seid includes both divination and manipulative magic. The type of divination practiced by seid was generally distinct by dint of an altogether more metaphysical nature than the day-to-day auguries performed by the seers (menn framsınir, menn forspáir).
In The Saga of Eric the Red, the seidkhona (or volva) in Greenland wore a blue cloak and a headpiece of black lamb with white catskins; carried the symbolic distaff (seidstafr), which was often buried with her; and would sit on a high platform, (this needs to be dealt with properly in terms of the concept of the frame). In Örvar-Odd's Saga, however, the cloak is black, yet the seidkhona also carries the distaff (which has the power (allegedly) of causing forgetfulness in one who is tapped three times on the cheek by it). The colour of the cloak is less significant than the fact that it was intended to signify the otherness of the seidkhona.
During seances the seidhkona would enter a trance state in which her soul was supposed to "become discorporeal", "take animal form", "travel through space", etc. This trance state may have been achieved through any of several methods: narcotics, sleep deprivation, sensory deprivation, etc.
An example of seid in Norse mythology is the trance undergone by the volva, Vala, or seeress in the prophetic vision given to Odin in the Voluspa. The interrelationship between the volva in this account and the Norns, the fates of Norse lore, are strong and striking.
The goddess Freya is seen as an adept of the mysteries of seid, and it is said that it was she who initiated Odin into its mysteries. In Lokasenna Loki abuses Odin for practising seid, condemning it as a unmanly art. A justification for this may be found in the Ynglinga saga where Snorri opines that following the practice of seid, the practitioner was rendered weak and helpless.
Some scholars (e.g. DuBois) draw a Saami and Balto-Finnic link to seid, citing the depiction of its practitioners as such in the sagas and elsewhere. In the Viking Age, seid was considered ergi (shameful) for men as its manipulative aspects ran counter to the male ideal of forthright, open behaviour.
Diana Paxson and her group, Hrafnar, have put in a lot of work reconstructing seid from available historical material, particularly its oracular form. Jan Fries traces seid as an inspiration for his "seething" shamanic technique, though he is less concerned with precise historical reconstruction.
Forms of Seid
The Practice of Seid
Seid in Mythology
Origins
Contemporary Reconstruction
Sources
See also: spae-craft