A set of tax principles can help in tax system design to better ensure administration, fairness, and economic efficiency. Like tax systems, tax principles should be evaluated regularly to ensure they address today's ways of living and doing business. This article discusses Tax Policy Concept Statement No. 1, Guiding Principles of Good Tax Policy: A Framework for Evaluating Tax Proposals (TPCS-1), which is the first in a series of AICPA statements, originally issued in 2001, intended to aid in the review and development of both existing tax rules and tax legislation.