Indian Revenue Service

This service deals with the matters concerning Income Tax. The members of this service, begin their career as Assistant Commissioners of Income Tax and may rise to the level of Chief Commissioners of Income Tax.
With changing times however, more and more IRS officers are serving in departments and areas that used to exclusively be the forte of IAS officers. This widening of opportunities and exposure has made the IRS more attractive.
Since there is no cadre system in this service you can expect to be posted anywhere in India nad even your home state, which becomes a problem for many in the IAS or IPS. The tenures are also more stable with an average of 3 years unlike the other two services where one may not even complete a month and the average tenure is around a year or so.
Officers of Indian Revenue Services (Income-tax) enter training at their academy at Nagpur. After training, they are posted as Assistant Commissioners either on assessment or other work.
While the main work of the department is assessment and recovery of direct taxes, the department has specialised branches dealing with investigation of tax evasion, statistics, and so on with the help of Assistant Directors (of the same rank as Assistant Commissioners of Income-tax). The Assistant Commissioners/ Deputy Directors, Communication Chief Commissioners become members of Central Board of Direct Taxes. The head of the department is the Chairman of the Central Board of Direct Taxes, who is invariably a member of the Indian Revenue Services (Income-tax). 

Indian Revenue Service Eligibility

The eligibility criteria for the Indian Revenue Service exam is the same as for other services. Once the candidate clears the civil services and gets allotment to the Indian foriegn service as per his rank, he has to go through specified training.