In this SHARE brief, Mathematica Senior Researcher, Cheryl Camillo, evaluates the Medicaid and CHIP eligibility changes that states will need to implement under the Affordable Care Act (ACA), identifying the most salient issues that states will need to consider in order to ensure that the new eligibility determination and renewal processes for these programs are effective.  The analysis is funded through a SHARE grant led by Mathematica's Dr. John Czajka and is the first in a series of three briefs titled "Eligibility Determination Using Modified Adjusted Gross Income: Implications for Enrollment under Heatlh Reform."