Tax avoidance is the legal usage of the tax regime in a single territory to one's own advantage to reduce the amount of tax that is payable by means that are within the law. Tax sheltering is very similar, although unlike tax avoidance tax sheltering is not necessarily legal. Tax havens are jurisdictions which facilitate reduced taxes.
Tax mitigation, "tax aggressive", "aggressive tax avoidance" or "tax neutral" schemes generally refer to multi-territory schemes that fall into the grey area between commonplace and well-accepted tax avoidance (such as purchasing municipal bonds in the United States) and evasion, but are widely viewed as unethical, especially if they are involved in profit-shifting from high-tax to low-tax territories and territories recognised as tax havens. Since 1995, trillions of dollars have been transferred from OECD and developing counties into tax havens using these schemes.
Laws known as a General Anti-Avoidance Rule (GAAR) statutes which prohibit "tax aggressive" avoidance have been passed in several developed countries including Canada, Australia, New Zealand, South Africa, Norway, Hong Kong and the United Kingdom. In addition, judicial doctrines have accomplished the similar purpose, notably in the United States through the "business purpose" and "economic substance" doctrines established in Gregory v. Helvering and in the UK through the Ramsay case. Though the specifics may vary according to jurisdiction, these rules invalidate tax avoidance which is technically legal but not for a business purpose or in violation of the spirit of the tax code. Related terms for tax avoidance include tax planning and tax sheltering.