There are those who believe in this grimoire, in its existence and in its potency, and there are those who do not.  Those who believe say that this grimoire, originally named Al Azif, and written by Abdul Alhazred around 700 AD, contains the rituals that, if performed correctly, will open the gates between this world and another, more sinister world, allowing the demons that once ruled this world to return and re-establish their rule.  

Accordingly, the rituals were given to Abdul Alhazred by a demon wishing that the rituals should be performed so that it might gain entry to this world. However, Abdul refused to perform the rituals and in Damascus, around 738 AD, he was set upon and eaten by this demon, causing the Al Azif to be lost from his guard.  Let loose upon the world, the Al Azif was translated into Greek by Theodorus Philetas of Constantinople, who named it the Necronomicon.  The Necronomicon was then translated into Latin by Olaus Wormius in 1228 and in 1232, Pope Gregory IX banned both the Greek and the Latin versions of the volume.  The original version, according to Wormius, was lost.  Years later, an English translation was made by Dr. John Dee, and it was this version that captured the intrigue of H.P. Lovecraft.

However, at the time that H.P. Lovecraft was writing at the beginning of the 20th century, the book did not really exist.  It was a complex fantasy, concocted by an author of a certain genius, who referred to the book in such a way as to make it seem as a genuine volume.  All that can be said to exist of the Necronomicon is the few 'quotes' that appeared in Lovecraft's writings.  Lovecraft was a member of the W.T. group of authors who made references to each other's fictitious tomes to create a background of illusion.  In his letter to Miss Margaret Sylvester on 13th January 1934, Lovecraft confesses that "This pooling of resources tends to build up quite a pseudo-convincing background of dark mythology, legendry, and bibliography."

Around the middle of the 20th century copies of the Necronomicon began to surface.  These texts were hugely sought after, although they were often only a few pages, translated and copied from surviving fragments of the original volumes.  The most famous of these, which was an almost complete copy, is what we now call the Simonomicon.  Like the authors of all the other copies, the text was based on the 'quotes' by Lovecraft, and then added to using the authors imagination, but uniquely in this case, also using Sumerian legend which added credibility and substance to the text.  However, just like all the other copies of the Necronomicon, the Simonomicon is a mere fabrication, a continuation of the mythos invented by Lovecraft years ago, and a tribute to his genius.