From Academy Bylaws:

Article III, Section 1.  Membership shall be by invitation of the Board of Governors.  Invitations to active membership shall be limited to those persons active in the motion picture arts and sciences, or credited with screen achievements, or who have otherwise achieved distinction in the motion picture arts and sciences and who, in the opinion of the Board, are qualified for membership.

Invitations to Associate Membership may be extended to those who have:
(a)   achieved distinction in their respective fields of endeavor in the theatrical motion picture industry for the past 8 years, but who do not qualify for branch membership or for Members-at-Large,
(b)  who have been owners or senior executives, for at least eight years, of organizations whose primary activities have contributed to the art or science of motion pictures,
(c)  who have made extraordinary contributions or performed unique services to the art or science of motion pictures.

Proposals must be accompanied by a letter from each sponsor which addresses, as specifically as possible, how the candidate meets one or another of the requirements above.
Associates, in accordance with Academy bylaws, are entitled to all benefits of Academy membership, including attendance at film showings and all special events. They do not participate in voting for Academy Awards and do not have direct representation on the Board of Governors.

The Board of Governors may transfer Active members to Associate status in accordance with Article III, Section 6 of the Academy Bylaws.

NOTE:  Please refer to special requirements for Artists' Representatives