The definition of assisted living varies from state to state and sometimes from residence to residence. Some states have used regulations or licensing requirements to define assisted living services. States using Medicaid HCBS waivers define the service to suit the purpose of their particular program. A variety of service delivery models are possible. The assisted living residence may be the provider of services, for example, or the service provider may be a separate agency. Yet a third alternative is to consider the assisted living setting a person's home; this permits a state to provide home and community services to persons in assisted living through the existing delivery system. Whatever the model chosen, it is important to note that assisted living in no way compromises a person's right to receive other Medicaid services. The overriding criterion for receipt of services under any model is medical necessity.