Permanent establishment: business fixed place rules define when cross-border activities create taxable presence under the treaty, with agent exceptions applying. A permanent establishment is a fixed place of business through which an enterprise's business is wholly or partly carried on, encompassing management offices, branches, factories, workshops, resource extraction sites, sales outlets, warehouses providing storage for others, and agricultural or plantation sites. Construction or installation projects constitute a permanent establishment when lasting more than six months. Purely preparatory or auxiliary activities - such as storage, display, purchasing, information collection or processing by another enterprise - do not create a permanent establishment. Dependent agents with authority to conclude contracts or who maintain stocks for regular delivery, and insurance activities through non-independent persons, can create a permanent establishment.