The Alzheimer’s Disease Neuroimaging Initiative 4 (ADNI4) study helps to understand Alzheimer’s disease by looking at things in the brain and body that might show if someone has the disease. It is a non-treatment study, which means participants won't receive any medication for Alzheimer's as part of the study. Instead, researchers will track changes in participants' brains and thinking abilities over time. Participants aged 55 to 90 can join if they are cognitively normal, have mild cognitive impairment (MCI), or dementia (DEM). Participants will have tests such as brain scans (like MRI and PET), and blood tests for up to 5 years. They will also have to visit one of the 59 study sites in the US or Canada. Some participants will be new, while others will continue from earlier studies. **Key Points:** - **Study Duration:** Up to 5 years with regular assessments. - **Eligibility:** Age 55-90, with or without memory concerns. - **Testing:** Includes brain scans, blood tests, and cognitive tests. For more details, visit the ADNI4 website [here](https://www.adni4.org/).