Place of supply rules determine tax location for services, defaulting to the registered recipient's location where available. Place of supply rules for domestic services default to the location of the registered recipient; for unregistered recipients the recipient's recorded address or, if unavailable, the supplier's location serves as proxy. Immovable-property-related services are taxed at the property's location, apportioned among States if the property spans multiple States. Physical-performance services, transportation, events, telecom, insurance and brokerage follow specified location rules and allocation mechanisms, with recipient billing records often determinative.