Inter state supply classification governs when cross border transactions and imports are treated as inter state for GST purposes. Inter state supply rules classify goods and services as occurring in the course of inter State trade or commerce where the supplier's location and place of supply are in different States or Union territories; imported goods and services are treated as inter State until crossing customs; and supplies from India to places outside India, supplies to or by Special Economic Zone developers or units, and taxable supplies not constituting intra State supplies are treated as inter State supplies.