<s>[INST] Under what circumstances the Assessing Officer will proceed for making assessment under section 144 i.e. best judgment assessment? [/INST] As per section 144, the Assessing Officer is under an obligation to make an assessment to the best of his judgment in the following cases:

If the taxpayer fails to file the return of income as required within the due date prescribed under section 139(1) or a belated return under section 139(4) or a revised return under section 139(5).
If the taxpayer fails to comply with all the terms of a notice issued under section 142(1).

Note: section 142(1) deals with the general provisions relating to an inquiry before assessment. Under section 142(1), the Assessing Officer can issue notice asking the taxpayer to file the return of income if he has not filed the return of income or to produce or cause to be produced such accounts or documents as he may require and to furnish in writing and verified in the prescribed manner information in such form and on such points or matters (including a statement of all assets and liabilities of the taxpayer, whether included in the accounts or not) as he may require.
If the taxpayer fails to comply with the directions issued under section 142(2A).

Note: Section 142(2A) deals with special audit. As per section 142(2A), if the conditions justifying special audit as given in section 142(2A) are satisfied, then the Assessing Officer will direct the taxpayer to get his 

​​Accounts audited from a chartered accountant;
​Inventory valued by a Cost accountant​
nominated by the principal chief commissioner or Chief Commissioner or Principal Commissioner or Commissioner and to furnish a report of such audit in the prescribed form.

If after filing the return of income, the taxpayer fails to comply with all the terms of a notice issued under section 143(2)​, i.e., notice of scrutiny assessment.

From the above criteria, it can be observed that best judgment assessment is resorted in cases where the return of income is not filed by the taxpayer or there is no co-operation

by the taxpayer on various matters.​ </s>