Anderson’s Constitution is the basis of Modern Freemasonry and its foundation of operation. A variety of stories and irregularities exist about its legitimacy and its foundation, yet, it remains an early canon of Masonic History.
For some background this excerpt from wikipedia offers some insight to its history:
The Constitutions of the Free-Masons was a constitution written for the Premier Grand Lodge of England, to standardize the rituals and practices of Freemasonry among lodges of London and Westminster operating under that Grand Lodge. Obviously, it was not meant to apply to other lodges in other parts of England, Scotland and Ireland. The constitution laid the foundation of the legend of Hiram Abiff, King Solomon’s Master Builder, along with the pyramid style organizational model of Freemasonry. The first and second edition were written by Rev. James Anderson in 1723 and 1738.