Tax Deduction and Collection Account Number is a 10 digit alphanumeric number, e.g. DELM12345L, required to be obtained by all persons who are responsible for deducting tax at source or collecting tax at source. It is compulsory to quote TAN in TDS/TCS return (including any e-TDS/TCS return), any TDS/TCS payment challan, TDS/TCS certificates, Annual Information Return and other documents as may be prescribed. There are two modes for applying for TAN- Offline and online.