Omicron Delta Kappa (ΟΔΚ), also known as The Circle and ODK, is an American collegiate honor society that recognizes leadership and scholarship. It was founded in 1914, at Washington and Lee University in Lexington, Virginia and has chartered more than 400 chapters or circles. To be selected as a member of ΟΔΚ, students must be among the top 35 percent of all students at that particular institution and hold a leadership role in one of the society's five areas of recognition. Omicron Delta Kappa is a member of the Honor Society Caucus, along with Phi Beta Kappa, Phi Kappa Phi, and Sigma Xi.

On December 3, 1914, the Omicron Delta Kappa Society was founded by fifteen men who met in an office on the third floor of Reid Hall at Washington and Lee University. J. Carl Fisher first introduced the idea of creating such a society to a close friend, Rupert Latture. The two soon included mutual friend William Brown in the discussion; these three are referred to as the principal founders of the society.

Together with the president of the university, the dean of engineering, and another faculty member, Fisher, Latture, and Brown selected nine others to join them. Omicron Delta Kappa's fifteen charter members were:

All fifteen men were prominent leaders on campus. They rallied around the idea that all-around leadership in college should be recognized, in all phases of college life.

The founders kept the organization secret until keys could be designed and produced. The keys arrived shortly past the winter holiday. The student newspaper, Ring-Tum Phi, broke the news on January 12, 1915, of a new society to be known as "The Circle," with the secret significance of its three Greek letters known only to its members. The members first wore their keys on January 15, 1915.

The society's first class of members were initiated at Washington and Lee in May 1915. In 1916, Omicron Delta Kappa became a national society with the establishment of Beta at Johns Hopkins University and Gamma at the University of Pennsylvania. It held its first national convention in 1920 at Johns Hopkins. By 1927, it has 17 circles or chapters with 1,500 members. It had grown to 106 circles and 38,660 initiates in 1963.

Only men could become members of Omicron Delta Kappa in the first sixty years of its existence. At the 1970 and 1972 national conventions, the University of Alabama Circle introduced an amendment to the national constitution to admit women into the society. In June 1972, Title IX prohibited sex discrimination in federally assisted educational programs and amended parts of the Civil Rights Act of 1964. Professional and honor fraternities were included in Title IX. Omicron Delta Kappa's special committee on the possible role of women met in January 1973 and recommended changes to the national constitution that would abolish segregation based on gender. On March 12, 1974, the national convention convened in New Orleans and approved the initiation of women into the society. The first women members were initiated that day, including Carolyn Julia Kucinski, and Diane Christine Ragosa of the Newark College of Engineering circle and Robbie Lynn Cooney, Maria Dolores Delvalle, Roxane R. Dow, Catherine Ann Rohrbacher, Karen Diane Janzer, Linda Ann Touten, Martha Gwyn Van Deman, and Cathy Sue Welch of the University of South Florida circle.

Cheryl Hogle was elected as the first woman national president at the national convention in Knoxville, Tennessee on February 25, 1998.