The fundamental purpose of a health insurance exchange is to provide a structured marketplace for the sale and purchase of health insurance. The authority and responsibilities of an exchange may vary, depending on statutory or other requirements for its establishment and structure. The Patient Protection and Affordable Care Act (ACA, P.L. 111-148, as amended) requires health insurance exchanges to be established in every state by January 1, 2014. ACA provides certain requirements for the establishment of exchanges, while leaving other choices to be made by the states. Qualified individuals and small businesses will be able to purchase private health insurance through exchanges. Issuers selling health insurance plans through an exchange will have to follow certain rules, such as meeting the private market reform requirements in ACA. While the fundamental purpose of the exchanges will be to facilitate the offer and purchase of health insurance, nothing in the law prohibits qualified individuals, qualified employers, and insurance carriers from participating in the health insurance market outside of exchanges. Moreover, ACA explicitly states that enrollment in exchanges is voluntary and no individual may be compelled to enroll in exchange coverage. Exchanges may be established either by the state itself as a "state exchange" or by the Secretary of Health and Human Services (HHS) as a "federally facilitated exchange." All exchanges are required to carry out many of the same functions and adhere to many of the same standards, although there are important differences between the types of exchanges. States will need to declare their intentions to establish their own exchanges by no later than November 16, 2012. ACA and regulations require exchanges to carry out a number of different functions. The primary functions relate to determining eligibility and enrolling individuals in appropriate plans, plan management, consumer assistance and accountability, and financial management. ACA gives various federal agencies, primarily HHS, responsibilities relating to the general operation of exchanges. Federal agencies are generally responsible for promulgating regulations, creating criteria and systems, and awarding grants to states to help them create and implement exchanges. A state that is approved to operate its own exchange has a number of operational decisions to make, including decisions related to organizational structure (governmental agency or a nonprofit entity); types of exchanges (separate individual and Small Business Health Options Program (SHOP) exchanges, or a merged exchange); collaboration (a state may independently operate an exchange or enter into contracts with other states); service area (a state may establish one or more subsidiary exchanges in the state if each exchange serves a geographically distinct area and meets certain size requirements); contracted services (an exchange may contract with certain entities to carry out one or more responsibilities of the exchange); and governance (governing board and standards of conduct). In general, health plans offered through exchanges will provide comprehensive coverage and meet all applicable private market reforms specified in ACA. Most exchange plans will provide coverage for "essential health benefits," at minimum; be subject to certain limits on cost-sharing, including out-of-pocket costs; and meet one of four levels of plan generosity based on actuarial value. To make exchange coverage more affordable, certain individuals will receive premium assistance in the form of federal tax credits. Moreover, some recipients of premium credits may also receive subsidies toward cost-sharing expenses.