In this dissertation I investigate and compare the impairments of long-lived operating assets under US Generally Accepted Accounting Principles (US GAAP) and International Financial Reporting Standards (IFRS) from different perspective, including the informativeness, determinants, and market valuation of asset impairments. A firm invests in long-lived operating assets with the expectation of generating future benefit. The decision or recognition of asset impairments implies such future benefit is expected to be lower than originally estimated. US GAAP and IFRS both require the recognition of impairment losses but their standards and accounting approaches are different in several ways. These distinctions raise the question whether the reported long-lived asset impairments under US GAAP and IFRS are comparable and motivate this dissertation. I investigate the predictive ability of reported asset write-offs for firms' future performance and find negative associations suggesting the informativeness of impairment losses. But such informativeness depends on the type of assets impaired, the accounting standards adopted, and the institutional characteristics. In general, aggregate impairments are persistently associated with future performance under IFRS but not US GAAP. The impairments of tangible assets have more predictive ability than those of intangibles. For IFRS adopters, enforcement takes a more important role in determining the informativeness of asset impairments than legal origins. I also examine the determinants and attributes of asset impairments under US GAAP and IFRS. I find both of them reflect certain economic factors and reporting incentives. Under US GAAP asset impairments strongly reflect GDP growth, unemployment rate, industry-trend and reporting incentives, including taking a big bath and income smoothing. Under IFRS the impairments reflect most economic factors but less reporting incentives. However, when enforcement is low in IFRS countries, firms tend to manage earnings through asset write-offs. I further address the market valuation of asset write-offs under US GAAP and IFRS. The reporting of asset impairments improves the explanatory power of accounting information for equity prices under IFRS but not US GAAP, especially when enforcement is high. The associations between asset write-offs and equity prices under IFRS in high enforcement countries are significantly different from those under US GAAP, implying investors weigh reported impairments under IFRS. I also use stock returns as an alternative metric of market valuation. Under US GAAP, asset write-offs are negatively associated with past, current, and future stock returns. Under IFRS in high enforcement countries the effects of impairment loss concentrate on past and current stock returns. The results of comparisons suggest asset write-offs under US GAAP and IFRS are not totally comparable from a market perspective. This dissertation contributes to literature on special items, impairment accounting, and reporting under IFRS. It is also related to the comparability of financial reporting under US GAAP and IFRS. While studies have compared overall properties of the two standards, examining the differences in a specific accounting area is also important as U.S. SEC express concern about the convergence of different accounting standards and whether U.S. should incorporate IFRS into its financial reporting systems. / Business Administration/Accounting