The Key of Solomon the King was originally researched and translated by S.L. MacGregor Mathers from ancient manuscripts in British museums. Included by Mathers is the Order of the Pentacles of Solomon, the Ancient Fragment of the Key of Solomon, The Qabalistic Invocation of Solomon, 15 plates full of figures, seals and charts, as well as the original text giving detailed instruction for spells and invocations.
The Lesser Key of Solomon, or the Clavicula Salomonis Regis, or Lemegeton, is a compilation of materials and writings from ancient sources making up a text book of magic or "grimeire" Portions of this book can be traced back to the mid-16th to 17th centuries, when occult researchers such as Cornelius Agrippa and Johannes Trithemisus assembled what they discovered during their investigations into their own great works.
As a modem grimoire, the Lesser Key of Solomon has seen several editions with various authors and editors taking liberty to edit and translate the ancient writings and source material. In 1898, Arthur Edward Waite published his The Book of Black Magic and of Pacts, which contained large portions of the Lemegeton. He was followed by Mathers and Crowley in 1904 who published The Goetia: The Lesser Key of Solomon. Many others have assembled their own version of this ancient material since, and it is important to realize that it is the contents rather than the book itself that make up the Lesser Key. Traditionally, the source material is divided into five books: Ars Goetia, Ars Theurgia Goetia, Ars Paulina, Ars Almadel, and Ars Notoria. Mathers and Crowley indicate their edition is a translation of the first.