There are over 100 extracurricular clubs and activities at Incheon International High School as of 2019. These clubs and activities are composed of three types: 15 academic clubs, 14 arts & sciences clubs, and 48 autonomous clubs. Time is allotted for the academic and arts & sciences clubs during the school day every week. As for the autonomous clubs, students are encouraged to organize and operate their own clubs, expanding their knowledge and collaborating with other students shared interests in the fields of their choice without explicit instruction from teachers.
As a high school which specializes in international subjects, IIHS focuses on developing students’ skills in the humanities, speech, and debate. While completing the regular curriculum, a variety of contests are offered to students. These include IIHS Debate Contests (Korean & English), IIHS Essay Contests (Korean & English), the IIHS Philosophy Olympiad (Korean & English), the IIHS Unification Golden Bell Contest, the IIHS Geography Olympiad, the IIHS Law Competition, the IIHS Politics & Sociology Essay Contest, the IIHS Korean History Contest, a Dok-do History Contest, the IIHS Foreign Languages Contest, and the IIHS Foreign Languages UCC Contest. The prize winners participate in local and national contests and have gone on to make outstanding achievements in the past.
Despite its recent creation in 2012, the IIHS floorball teams (mens and womens) have achieved brilliant results. In 2012, the men’s floorball team won 1st place in the junior group stage of the National Sports Festival. The womens team took a highly contested 2nd place. The mens and womens teams each won the 1st prize in the Incheon Superintendent Floorball competition, and both took bronze medals in the National School Sports Club Competition.
The Students' Autonomous Court is operated solely by students. Its goals are the following: to practice student- centered school guidance; to raise community spirit, responsibility ,and credibility: to ensure students' rights are respected and upheld; and to discover and enact preventive rather than punitive measures that deal with problem-causing situations. This court consists of three judges (one teacher & two students), four prosecutors, sixteen attorneys, four assistants, and fifteen jurors.