The dictionary meaning of the term "audit" is check, review, inspection, etc. There are various types of audits prescribed under different laws like company law requires a company audit, cost accounting law requires a cost audit, etc. The Income-tax Law requires the taxpayer to get the audit of the accounts of his business/profession from the view point of Income-tax Law.

Section 44AB gives the provisions relating to the class of taxpayers who are required to get their accounts audited from a chartered accountant. The audit under section 44AB aims to ascertain the compliance of various provisions of the Income-tax Law and the fulfillment of other requirements of the Income-tax Law. The audit conducted by the chartered accountant of the accounts of the taxpayer in pursuance of the requirement of section 44AB is called tax audit.

The chartered accountant conducting the tax audit is required to give his findings, observation, etc., in the form of audit report. The report of tax audit is to be given by the chartered accountant in Form Nos. 3CA/3CB and 3CD. 

One of the objectives of tax audit is to ascertain/derive/report the requirements of Form Nos. 3CA/3CB and 3CD. Apart from reporting requirements of Form Nos. 3CA/3CB and 3CD, a proper audit for tax purposes would ensure that the books of account and other records are properly maintained, that they truly reflect the income of the taxpayer and claims for deduction are correctly made by him. Such audit would also help in checking fraudulent practices. It can also facilitate the administration of tax laws by a proper presentation of accounts before the tax authorities and considerably save the time of Assessing Officers in carrying out routine verifications, like checking correctness of totals and verifying whether purchases and sales are properly vouched for or not. The time of the Assessing Officers saved could be utilised for attending to more important and investigational aspects of a case.​

As per section 44AB, following persons are compulsorily required to get their accounts audited:

• A person carrying on business, if his total sales, turnover or gross receipts (as the case may be) in business for the year exceed or exceeds Rs. 1 crore. This provision is not applicable to the person, who opts for presumptive taxation scheme under section 44AD​ and his total sales or turnover does not excceeds Rs. 2 crores.

• A person carrying on profession, if his gross receipts in profession for the year exceed Rs. 50 lakhs.

• A person who is eligible to opt for the presumptive taxation scheme of section 44AD but claims the profits or gains for such business to be lower than the profits and gains computed as per the presumptive taxation scheme of section 44AD and his income exceeds the amount which is not chargeable to tax.

• If an eligible assessee opts out of the presumptive taxation scheme, after specified period, he cannot choose to revert back to the presumptive taxation scheme for a period of five assessment years thereafter.

• ​A person who is eligible to opt for the presumptive taxation scheme of section 44ADA  but he claims the profits or gains for such profession to be lower than the profit and gains computed as per the presumptive taxation scheme and his income exceeds the amount which is not chargeable to tax.

• A person who is eligible to opt for the presumptive taxation scheme of sections 44AE but he claims the profits or gains for such business to be lower than the profits and gains computed as per the presumptive taxation scheme of sections 44AE.

• A person who is eligible to opt for the taxation scheme prescribed under section 44BB  or section 44BBB  but he claims the profits or gains for such business to be lower than the profits and gains computed as per the taxation scheme of these sections.

Section 44BB is applicable to non-resident taxpayers engaged in the business of providing services or facilities in connection with, or supplying plant and machinery on hire basis to be used in exploration of mineral oils. section 44BBB​ is applicable to foreign companies engaged in the business of civil construction or erection of plant or machinery or testing or commissioning thereof, in connection with a turnkey power project.

The report of the tax audit conducted by the chartered accountant is to be ​furnished in the prescribed form. The form prescribed for audit report in respect of audit conducted under section 44AB​ is Form No. 3CB and the prescribed particulars are to be reported in Form No. 3CD.In case of persons covered under previous FAQ, i.e., who are required to get their accounts audited by or under any other law, the form prescribed for audit report is Form No. 3CA/3CB and the prescribed particulars are to be reported in Form No. 3CD.​

The report of the tax audit conducted by the chartered accountant is to be ​furnished in the prescribed form. The form prescribed for audit report in respect of audit conducted under section 44AB​ is Form No. 3CB and the prescribed particulars are to be reported in Form No. 3CD.In case of persons covered under previous FAQ, i.e., who are required to get their accounts audited by or under any other law, the form prescribed for audit report is Form No. 3CA/3CB and the prescribed particulars are to be reported in Form No. 3CD.​

A person covered by section 44AB should get his accounts audited and should obtain the audit report on or before the due date of filing of the return of income, i.e., on or before 30th September (*) of the relevant assessment year, e.g., Tax audit report for the financial year 2017-18 corresponding to the assessment year 2018-19 should be obtained on or before 30th September, 2018.

(*) In case of a taxpayer who is required to furnish a report in Form No. 3CEB under section 92​ in respect of any international transaction or specified domestic transaction, the due date of filing the return of income is 30th November of the relevant assessment year.

According to section 271B, if any person who is required to comply with section 44AB fails to get his accounts audited in respect of any year or years as required under section 44AB, the Assessing Officer may impose a penalty. The penalty shall be lower of the following amounts:

(a) 0.5% of the total sales, turnover or gross receipts, as the case may be, in business, or of the gross receipts in profession, in such year or years.

(b) Rs. 1,50,000.

However, according to section 273B​, no penalty shall be imposed if reasonable cause for such failure is proved.