Today, the word "mafia" is used to refer to almost any organized crime group, and in some cases is even used to describe groups completely unrelated to crime. In this article, we will focus on the traditional meaning of "mafia": organized criminal organizations of Italian or Sicilian heritage.
In organized crime there is a hierarchy, with higher-ranking members making decisions that trickle down to the other members of the family. The Mafia is not a single group or gang -- it is made up of many families that have, at times, fought each other in bitter, bloody gang wars. At other times, they have cooperated in the interest of greater profits, sometimes even serving on a "Commission" that made major decisions affecting all the families (more on the Commission later). Most of the time, though, they simply agree to stay out of each other's way.
Mafia-dom is neither a political nor a religious affiliation. Because of their Italian roots, many Mafioso are Catholic, but part of the oath a mobster takes when he becomes a "made man" -- a member of a Mafia family -- is that the Mafia comes before birth family and God.