I class may refer to:
Acheron-class destroyer, a class of destroyers that served in World War I I-class destroyer, a class of destroyers of the 1930s I-class ferry, a class of ferries operated by BC Ferries Istanbul-class frigate, a late 2010s class of indigenous Turkish frigates South Australian Railways I class (first), 0-4-0T steam locomotive South Australian Railways I class (second), 0-4-0ST steam locomotive WAGR I class, 0-6-4T steam locomotive
See also Class I (disambiguation)