GST applicability clarifies time of supply, reverse charge obligations, registration triggers and transitional input credit rules. Clarifies GST operative rules on time of supply, place of supply, reverse charge, registration thresholds and transitional input tax credits. Time of supply governs liability regardless of payment; suppliers must issue invoices within prescribed time and recipients may pay under reverse charge where notified, with input tax credit available for tax so paid. Place of supply rules determine intra or inter state character and zero rating when proceeds are realized in convertible foreign exchange. Registration is required in specified circumstances including inter state supplies and supplies through e commerce operators; deemed transitional credits for stock and WIP are allowed subject to conditions.