Permanent establishment: treaty rules identify fixed business places and agency activities that create taxable presence abroad. Permanent establishment is a fixed place of business through which an enterprise's business is wholly or partly carried on, including management offices, branches, factories, workshops, sales outlets, warehouses for others, farms and places of extraction. Building sites and construction or installation projects and furnishing of services by personnel qualify when they exceed specified duration thresholds. Exclusions cover solely storage, display, stock for processing, purchasing, information collection and preparatory or auxiliary activities. Agency rules treat non independent agents who habitually conclude contracts, maintain stock for delivery, or secure orders as creating a permanent establishment; independent agents acting in the ordinary course do not.