Tax Law

Westlaw, Lexis, and Bloomberg have separate databases for just tax law. 

Westlaw's Tax Page

Lexis' Tax Page

Bloomberg's Tax Page

Those three major publishers also have Tax Court opinions, but their coverage can be spotty for the unpublished/memoranda TC decisions.

You can also find Tax Court decisions on the Tax Court's website:  ustaxcourt.gov

A refresher from the Main Sources of Tax Law page.  Some big sources of tax jurisprudence are:

• United States Supreme Court
• Federal appellate courts (aka, the Circuit Courts)
• US federal district courts
• Tax Court.  They issue three types of opinion:
  • Regular/Formal Opinions.  Also called TC Opinions or Division Opinions.  This is the kind of judicial opinion we're used to.  Published in the Tax Court Reports, they are binding, precedential, and appealable. 
  • Memorandum (TC Memos or Memo Opinions).  Unpublished, but are still cited.
  • Summary decisions.  Kind of like the 'small claims court' of tax law.  Involves controversies below $50,000.  Not precedential.

Abbreviations

AFTR:  American Federal Tax Reports.  They're published by RIA.

BTA Mem. Dec. OR BTAM:  Board of Tax Appeals Memorandum Decisions

TC:  Tax Court

TCM:  Tax Court Memorandum Decisions

TCR:  Tax Court Reporter.  They're published by CCH or RIA.

USTC:  United States Tax Cases

Citations

Bluebook

• Tax Court:  BT2.1 (p. 46 in the 21st ed.)
• Board of Tax Appeals: T1  (particularly p. 237 in the 21st ed.)

ALWD

• Tax Court: Appendices 6(B) and 6(B)(1) (page 506-508 in the 7th ed.)