A range of courts–including the U.S. Tax Court, U.S. Ct. of Fed. Claims, U.S. District Courts., and U.S. Appeal Courts.–adjudicate disputes involving federal taxation. So, databases publishing the decisions of these courts will offer judicial opinions relating to federal tax issues.

The U.S. Tax Court issues three types of decisions:

• Formally published decisions: Also called TC Opinions or "division opinions." They are published in the Tax Court Reports.
• Memorandum decisions:  Also called TC Memos or Memo Opinions: They are unpublished decisions, generally involving already settled legal issues. They are still often cited though.
• Summary decisions These decisions involve controversies of below $50,000. They are not precedential.

Fore more information, see McDermott's very helpful Types of Tax Court Opinions and Their Precedential Effect

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