BiCollege cooperation allows Bryn Mawr students to major at Haverford, and Haverford students to major at Bryn Mawr. At Haverford, major declaration is limited to the spring semester, so Bryn Mawr students will not be allowed to officially declare a Haverford major until the spring. Haverford also does not use the same online process as Bryn Mawr does. Soon after spring break, Bryn Mawr sophomores will receive information that outlines the procedures for declaring a major at Haverford. For your reference, here are recent instructions from the Haverford Dean's Office.
If you are debating between the Bryn Mawr and Haverford departments in a particular field, be sure to talk with faculty members and declared majors in each department.