Dependents fall into two categories, a qualifying child or a qualifying relative. In order to claim an adult dependent, they must pass these seven tests:
Dependent Taxpayer Test
Joint Return Test
Citizen or Resident Test
Qualifying Child Test
Member of Household or Relationship
Gross Income Test
Support Test
To find out if you can cut your tax bill by claiming an adult dependent, visit the AARP article, 6 Tax Breaks If You Have an Adult Dependent.