1. Relationship: The person must be your child, stepchild, foster child, sibling, step-sibling, or a descendant of any of them (e.g., grandchild). They can also be your niece, nephew, or certain other relatives in specific cases. There are also rules for claiming a qualifying relative who may not be directly related to you.
2. Citizenship or Resident: The dependent must be a U.S. citizen, U.S. resident alien, U.S. national, or a resident of Canada or Mexico.
3. Support: You must have provided more than half of the dependent's financial support during the tax year. This includes costs for housing, food, clothing, medical care, education, and other necessities.
4. Income: Generally, the dependent must have had less than a certain amount of gross income during the tax year. This income threshold changes annually and depends on the type of income, age, and filing status.
5. Filing Status: If the dependent is married and filing a joint return with their spouse, they generally cannot be claimed as a dependent unless they're filing the joint return only to claim a refund and would have no tax liability if filing separately.

There are some additional rules and exceptions for specific situations, such as divorced or separated parents, multiple support agreements, and special cases for qualifying relatives. It's important to consult the IRS guidelines or a tax professional to ensure you meet all the requirements for claiming a dependent on your tax return.