The aim of the Health and Retirement Study (HRS) Harmonized Cognitive Assessment (HCAP) project is to create a new HRS data resource to better assess the current and future trends in mild cognitive impairment (MCI) and dementia in the United States. The first HRS sub study on dementia, the Aging, Demographics, and Memory Study (ADAMS) provided the first estimates of dementia incidence and prevalence in the United States using a nationally representative sample. The new Harmonized Cognitive Assessment Protocol (HCAP) project builds on the experience and methods of the HRS and ADAMS for studying cognition, cognitive decline, and dementia. The main strategy is to administer an expanded battery of cognitive tests and informant interviews to a random subsample of HRS respondents aged 65 and older. The first wave of HRS/HCAP participants was fielded in 2016.