Health care financing refers to the means in which health care is funded. The process includes three basic functions: 1) revenue collection, 2) risk pooling, and 3) purchasing health services and payment methods. Major concerns in relation to revenue collection include how, and from which sources, to collect money that will sufficiently finance health care in an equitable and sustainable way. Health services can be financed directly, at the time of service utilization, by out-of-pocket payment or through a prepaid system. Out-of-pocket payments are common in most developing countries and often finance health services in the private sector.