Duty liability in job work determines which party bears excise responsibility after processing under Cenvat or notification regimes. Job work is processing of supplier provided inputs by a job worker; excise duty arises only if those processes amount to manufacture. Where manufacture occurs and no Cenvat or exemption applies, duty liability rests with the job worker and the assessable value is the value of the final product - raw material cost plus job charges (including processing expenses and the job worker's profit) and specified additional considerations; certain costs (supplier's trading profit, duty on inputs where Cenvat is available, brand value, technical know how) are excluded.