| Ilkley Playhouse | Ilkley Playhouse | 2024 | 1 | |
| Illini Theatre Guild Laboratory Theatre, The | The Illini Theatre Guild Laboratory Theatre | 1947 – 1949 | 4 | |
| Illinois Repertory Theatre University of Illinois | Illinois Repertory Theatre University of Illinois | 1988 | 1 | |
| Incorporated Stage Society | Incorporated Stage Society | 1906 | 1 | |
| Independent Company, The | The Independent Company | 1899 | 1 | |
| Independent Theatre Society, The | The Independent Theatre Society | 1891 – 1997 | 14 | |
| Independent Theatre, The | Independent Theatre (The Independent Theatre) | 1946 – 2023 | 2 | |
| Indiana University Department of Theatre and Drama | Indiana University Department of Theatre and Drama | 1979 – 2019 | 3 | |
| Infamous Commonwealth Theatre | Infamous Commonwealth Theatre | 2011 | 1 | |
| Ingun Bjørnsgaard Prosjekt | Ingun Bjørnsgaard Prosjekt | 2010 – 2014 | 5 | |
| Innervoice Media | Innervoice Media | 2021 | 1 | |
| Institutt for drama/film/teater | Institutt for drama/film/teater | 1994 | 1 | |
| Intercity Festival Oslo | Intercity Festival Oslo | 2009 | 1 | |
| Internasjonale Figurteaterfestival, Den | Den Internasjonale Figurteaterfestival | 1992 – 1993 | 1 | |
| International Ibsen | International Ibsen | 2010 | 1 | |
| International Ibsen Conference, The | The International Ibsen Conference | 2006 | 1 | |
| International Ibsen Festival 2010 | International Ibsen Festival 2010 | 2010 | 3 | |
| International Ibsen Festival for University Students | International Ibsen Festival for University Students | 2010 | 3 | |
| International Ibsen Seminar and Theatre Festival | International Ibsen Seminar and Theatre Festival | 2009 – 2012 | 3 | |
| International Ibsen Stage Festival | International Ibsen Stage (International Ibsen Stage Festival) | 2012 – 2013 | 16 | |
| International Theatre Festival | International Theatre Festival | 2004 | 2 | |
| Internationale Maifestspiele | Internationale Maifestspiele | 1954 – 2003 | 3 | |
| internationale Tournée Gustav Lindemann, Die | Die internationale Tournée Gustav Lindemann | 1903 – 1904 | 13 | |
| Internationale Tournee Maria Rehoff | Internationale Tournee Maria Rehoff | 1904 – 1912 | 85 | |
| Intervención Ibsen | Intervención Ibsen | 2016 | 4 | |
| Interzona and La Biennale di Venezia | Interzona (Interzona and La Biennale di Venezia) | 1999 – 2000 | 6 | |
| Intimes Theater | Intimes Theater | 1909 | 1 | |
| IPFW Department of Theatre | IPFW Department of Theatre | 2008 – 2014 | 2 | |
| Ireland Drama Festival | Ireland Drama Festival | | | |
| Irving Place Company | Irving Place Company | 1917 | 1 | |
| Isac Fredrik Smitts sällskap | Isac Fredrik Smitts sällskap | 1877 – 1880 | 12 | |
| ITESM Unidad Chihuahua | ITESM Unidad Chihuahua | 1985 | 1 | |
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