Input tax credit transition: admissible pre GST credits migrate to the electronic ledger subject to filing and substantiation requirements. Transitional rules allow registered persons (excluding composition taxpayers) to carry forward admissible CENVAT/VAT credits from the last pre GST return into the electronic credit ledger subject to conditions: admissibility under GST, filing of required returns for the six months before the appointed day, and exclusions for specified notified clearances; SGST imposes further limits on CST linked claims unless substantiated. Inputs, capital goods and job work goods returned within six months (extendable for cause) avoid GST recovery; failure to return triggers ITC recovery. Pending refunds and appeals under prior law continue under that law, though recoverable amounts may be recovered as GST arrears.