Satisfactory completion of a major field is required. Most departmental programs require a minimum of 32 credits, but may include more. At the department's discretion, up to 8 credits from related fields may be counted toward the major. The requirements for each major program are listed in Courses of Study. Academic departments normally expect that the majority of courses constituting the major, and all required courses, will be completed at Grinnell.

A student declares a major before preregistration for the fifth semester and is held to all major requirements in effect at the time of declaration. The head of the department in which the major is declared, or a designated colleague, then becomes the student's adviser. Most students choose a departmental or an interdepartmental major. However, a student may arrange a special program as an independent major or may be permitted a second major.