Valuation under GST defines transaction value and valuation methods for non monetary, related party and special supplies, including agency and pure agent rules. Valuation under GST treats transaction value as the primary basis when parties are unrelated and price is sole consideration, including amounts the supplier must pay but the recipient incurred, and excluding specified refundable deposits and qualifying pre supply discounts. If consideration is non monetary or parties are related, valuation follows a hierarchy: open market value, monetary consideration plus monetary equivalent of non monetary consideration, value of like kind and quality supplies, cost based rule, and finally a residual reasonable means method.