This study examines the use of teacher and student humor in the English-as-a-Second-Language (ESL) classroom. A summary and synthesis of previous research on theories of humor, humor and its use in society, and applications of humor revealed its importance as an object of study. An analysis of audiotaped transcripts of samples of ESL classes yielded the following results: (1) approximately one-third of all classroom humor is student-initiated; (2) student humor was similar from class to class, while teacher-initiated humor varied considerably; (3) both students and teachers used exaggeration, contrast, and emotion, although students used exaggeration far more than any other kind of humor; and (4) students laugh at the vast majority of humor in the classroom, though they are more inclined to laugh at humor initiated by their peers than by their teachers. (Author/JL)