Occupational Therapy Association of California, The Occupational Therapy Association of California (OTAC) was incorporated in 1976 as the result of a merger of the southern and northern California groups. It is a not-for-profit, 501-c-6 professional society designed to be the collective voice that serves, promotes, and supports the more than 15,000 occupational therapists (OTs) and occupational therapy assistants (OTAs) throughout California.