The private health insurance provisions in the Patient Protection and Affordable Care Act (P.L. 111-148, ACA, as amended) include market reforms that impose requirements on private health insurance plans. Such reforms relate to the offer, issuance, generosity, and pricing of health plans, among other requirements. ACA's market reforms largely focus on the individual and small group health insurance markets, and in this report the reforms have been grouped by effective dates: "immediate" market reforms that become effective prior to the full implementation date of ACA, and reforms that become effective on the full implementation date (January 1, 2014). ACA requires implementation of a number of reforms prior to its full implementation date (i.e., prior to plan years beginning on or after January 1, 2014). "Immediate" reforms include a process to review unreasonable rate increases; an Internet portal to assist consumers in identifying coverage options; prohibition on lifetime limits and restriction of annual limits; the prohibition on rescissions; coverage of preventive health services with no cost-sharing; extension of dependent coverage; prohibition of discrimination based on salary; standards related to medical loss ratios and rebates to plan participants; appeals process; coverage of preexisting health conditions for children; patient protections; uniform explanation of coverage documents; and reporting requirements regarding quality of care. Market reforms effective beginning in 2014 include nondiscrimination based on health status; guaranteed issue and guaranteed renewability; coverage of preexisting health conditions (regardless of age); nondiscrimination regarding clinical trial participation; rating restrictions; waiting period limitation; and nondiscrimination regarding health care providers. This report provides background information about the private health insurance market, including market segments and regulation. It describes each ACA market reform and notes any major implementation activity that has occurred (e.g., issuance of final rule from a department such as Health and Human Services). The appendices of the report provide additional information about the status of regulations relating to each reform and how the reforms apply to the different market segments and health plans.