The absolute minimum requirement of any body of Freemasons is that the candidate must be free, and considered to be of good character. There is usually an age requirement, varying greatly between Grand Lodges, and (in some jurisdictions) capable of being overridden by a dispensation from the Grand Lodge. The underlying assumption is that the candidate should be a mature adult.
Additionally, most Grand Lodges require the candidate to declare a belief in a Supreme Being. In a few cases, the candidate may be required to be of a specific religion. The form of Freemasonry most common in Scandinavia (known as the Swedish Rite), for example, accepts only Christians. At the other end of the spectrum, “Liberal” or Continental Freemasonry, exemplified by the Grand Orient de France, does not require a declaration of belief in any deity, and accepts atheists (a cause of discord with the rest of Freemasonry).
(the source/read more: Wikipedia)