The Knights of Columbus (K of C) is a global Catholic fraternal service order founded by Michael J. McGivney on March 29, 1882. Membership is limited to practicing Catholic men. It is led by Patrick E. Kelly, the order's 14th Supreme Knight.The organization was founded in March 1882 as a mutual benefit society for working-class and immigrant Catholics in the United States. It has grown to support refugee relief, Catholic education, local parishes and dioceses, and global Catholic social and political causes. The Knights promote the Catholic view on public policy issues, including opposition to same-sex marriage and abortion. Between 2008 and 2012, K of C gave at least $15 million to lobbies opposed to same-sex marriage.: 1 The organization also provides certain financial services to the individual and institutional Catholic market. Its wholly owned insurance company, one of the largest in the world, underwrites more than two million insurance contracts, totaling more than $100 billion of life insurance in force. The order also owns the Knights of Columbus Asset Advisors, a money management firm which invests in accordance with Catholic social teachings.

As of 2019, there were nearly two million members around the world. Women may participate in K of C through the Columbiettes and other female auxiliaries, and boys may join the Columbian Squires. The Order comprises four different "degrees", each one of which exemplifies one of the core principles of the order. There are more than 16,000 local Knights of Columbus councils around the world, including over 300 on college campuses.