PIP: The Immigration Reform and Control Act of 1986 attempts to curb unauthorized migration by requiring employers to screen the authorizing documents of all workers. Many different documents may be used, with employers required to simply attest to the face validity of workers' documents upon an I-9 form. The authors report findings from their study estimating the unauthorized US labor force and exploring employers' initial reactions to the passage of the Immigration Reform and Control Act (IRCA) of 1986. The findings are based upon hiring practices information supplied by a sample of businesses in an evaluation of the IRCA impact. A selectivity correction model is used to impute 2.6 million unauthorized workers in the entire sample. The estimate, which compares favorably with other estimates, is tabulated by questions about IRCA. Findings suggest that a large proportion of the unauthorized labor force uses fraudulent documents, many without the knowledge of their employer. It appears that Immigration and Naturalization Service-targeted establishments hire 20% of unauthorized workers and that the employers of unauthorized workers are no more likely than other employers to believe that they can be sanctioned under IRCA. This may be associated with the apparent lack of marked change in patterns of unauthorized hiring in the period immediately following IRCA passage. There was some change in hiring behaviors in establishments hiring unauthorized workers, affecting wage offers and documentation, but US employers do not seem to perceive changes in the supply or availability of authorized workers. Study findings indicate only marginal IRCA-related changes in the characteristics of unauthorized hires during the very initial phase of IRCA's implementation. The combination of readily available fraudulent documents, the difficulty in detecting such documents, and the steady demand for low-skilled workers creates conditions which are not conducive to markedly changed hiring behavior.