What is the origin and history of the Celtic knot?

Well first of all you'd have to figure out what a celt is many cultures such as the leTene or Halstat had their own knotwork designs so did the Norse and their is even the Jewish lyre knot which is based on the the Jewish harp.

While no-one is exactly sure why they developed the historical evidance points to them coming into existence from around 500 bc onwards.

Many of the websites listed below go into futher detail on the history of tribal knots.

http://www.museangel.net/knot.HTML

http://altreligion.about.com/library/glossary/symbols/bldefscelticknots.htm

http://en.wikipedia.org/wiki/Celtic_knot

http://www.thinkythings.org/knotwork/knotwork-meaning.HTML

http://www.aon-Celtic.com/trade_history_meanings.HTML

I hope this helps you.