Service tax registration: mandatory online ST-1 filing, centralised registration rules, amendment and surrender obligations enforce compliance. Every person liable to pay service tax must apply for registration in Form ST-1 within prescribed time and manner, file online through ACES and submit specified documents for verification; registration is free and subject to conditions. Centralised registration is available where centralised billing or accounting exists, and single registration may cover multiple services and premises. Registration certificates are not transferable; amendments must be notified within thirty days. Surrender is required on cessation of taxable services, and penalty may apply for failure to register.