In the last five years, U.S. generally accepted accounting principles ("U.S. GAAP") have undergone a significant transformation to a fair value reporting standard. Acquisitions are accounted for under purchase accounting rules under which acquired intangible assets are identified and valued separately. U.S. GAAP outlines five general categories of intangible assets. Intangible assets with an indefinite life and any remaining goodwill are not amortized, but rather are subject to periodic impairment testing. Goodwill impairment testing requires the valuation of a company's reporting units. Recent financial reporting valuation engagements include: