http://en.wikipedia.org/wiki/Catholicism_and_FreemasonryThere is much more but I snipped this:
Post Vatican II
After Vatican II, the Church appeared to some to be easing its stance towards Masonry. In 1974 Cardinal Seper, Prefect of the Congregation for the Doctrine of the Faith, signed a document that stated, in part, that
"The Sacred Congregation for the Doctrine of the Faith... has ruled that Canon 2335 no longer automatically bars a Catholic from membership of masonic groups... And so, a Catholic who joins the Freemasons is excommunicated only if the policies and actions of the Freemasons in his area are known to be hostile to the Church ..."<24>
This advice led some Catholics to believe that the prohibition was no longer in force,<25> and that the Church no longer had many of its traditional objections to Freemasonry.<26>
In 1983, the Church issued a new Code of Canon Law. Unlike its predecessor, Canon 1374 does not explicitly name Masonic orders among the secret societies it condemns. It states in part:
A person who joins an association which plots against the Church is to be punished with a just penalty; one who promotes or takes office in such an association is to be punished with an interdict.
This omission caused some Catholics and Freemasons to believe that the ban on Catholics becoming Freemasons may have been lifted, especially after the perceived liberalization of Vatican II,<27> and caused confusion in the Church hierarchy.<28> Many Catholics joined the fraternity, basing their membership on a permissive interpretation of Canon Law and justifying their membership by their belief that Freemasonry does not plot against the Church.<29> It is claimed that Catholic Freemasons in America ignore the 1983 clarification from the Vatican, looking to the 1974 pronouncement.<30>
Ratzinger's reply
However, in the 1981 letter, Clarification concerning status of Catholics becoming Freemasons to the United States Bishops from the Congregation for the Doctrine of the Faith authored by the then-Cardinal Joseph Ratzinger (now Pope Benedict XVI), the matter was clarified, and the prohibition against Catholics joining Masonic orders remains.
This was followed by the 1983 document Quaesitum est, issued by Pope John Paul II. To quote:
"The faithful, who enroll in Masonic associations are in a state of grave sin and may not receive Holy Communion..."<31>
This is the authoritative interpretation of the Vatican's position on this subject.
The official Vatican newspaper L'Osservatore Romano went further, claiming that Freemasonry acted as a rival to Catholicism because of the competing symbolic forms and the designation of Catholic non-Masons as outsiders.<32>