The Sons of Liberty was an organization of American patriots that originated in the North American British colonies. The group was formed to protect the rights of the colonists and to take to the streets against the abuses of the British government. They are best known for undertaking the Boston Tea Party in 1773 in reaction to the Tea Act, which led to the Intolerable Acts (an intense crackdown by the British government), and a counter-mobilization by the Patriots.
Sources: http://en.wikipedia.org/wiki/Sons_of_liberty, http://www.ushistory.org/declaration/related/sons.htm