The Berkeley Aging Cohort Study (BACS) is a longitudinal study designed to investigate how our brains change as we age. Participants are drawn largely from Berkeley and surrounding areas. These individuals undergo cognitive tests, fill out numerous questionnaires about health history and lifestyle, and are asked to return for periodic follow-up examinations. Select participants undergo longitudinal amyloid PET and tau PET imaging as well as MRI scans. The cohort was established over 10 years ago and has been studied intensively by members of the Jagust Lab including many graduate students and postdoctoral fellows. We also actively collaborate with other laboratories on the Berkeley campus, and many of our participants have been involved in studies of dopamine, sleep, and other studies. The cohort continues to expand with data from new and returning participants.