The Ontario Student Debating Union is a charitable organization that hosts and promotes competitive debate for Ontario students up to Grade 12. OSDU organizes a Provincial Championship every spring as well as a variety of regional debates and workshops. It also works with the Canadian Student Debating Federation and helps select students to represent Ontario at national and international debating events.

OSDU is steered by a board of directors, who are elected at the Annual General Meeting. Directors vote on matters discussed at board meetings and appoint officers, who fulfill the functions of President, Vice-President, Treasurer, Secretary, Membership Coordinator, and Director of French and Bilingual Debate. Two student representatives, one English and one French or bilingual, are elected annually by their peers at the Provincial Championship. Governors are non-voting advisory members of the board.

The province is divided into geographical regions to facilitate local debate and ensure that diverse areas are represented at provincial events. Regional coordinators are responsible for fostering debate in their regions, serving as a liaison between member schools and the board of directors, and organizing a regional qualifier each year that determines which students from their regions will advance to the Provincial Championship.

OSDU also facilitates debate for elementary and Junior High School students. A Junior Provincial Championship is held annually for students in grades 6 – 8, and the top speakers are eligible to represent Ontario at either the annual National Seminar, organized by the Canadian Student Debating Federation, or the Junior National Championship.

OSDU aims to make debate accessible to all Ontario students. In order to participate in OSDU events and have full access to the resources it offers, schools must pay a nominal fee and register as members with OSDU at the beginning of each academic year. Registration usually closes in mid-November. All membership issues are handled by the Membership Coordinator. Students may not register as individuals; only schools (or in special cases school boards) can become members.

OSDU is a registered charity. Its activities are funded entirely by membership fees, tournament registration fees, and charitable donations. All directors, coordinators, governors, and tournament chairs perform their duties on a strictly volunteer basis.