People of all ages, ethnicities, and racial backgrounds can volunteer for clinical trials. If you want to join a clinical trial, you must meet eligibility critera to participate in that specific trial. Your eligibility can usually be determined by phone or online screening. All clinical trials have eligibility guidelines called inclusion and exclusion criteria. These criteria may include: Age Sex The type and stage of an illness Treatment history Other medical conditions Researchers use these guidelines to find suitable study participants, maximize participant safety, and ensure trial data are accurate.