Mortimer M. Caplin, just resigned Commissioner of Internal Revenue, has been "your friendly tax collector" for over 3 1/2 years. Unlike most Commissioners, he became a well-known figure to almost every taxpayer. He has also been a controversial figure, blamed often for law changes (like the travel and entertainment rules) over which he had no control and for bringing "Big Brother" into everyone's life in the form of the "Martinsburg Monster": the ADP Master File at Martinsburg, W. Va., which will consume taxpayer account numbers and information returns and produce audit notices for the dishonest or careless taxpayer. Commissioner Caplin has always emphasized the human element in tax administration and the fundamental honesty of taxpayers who voluntarily pay in such a vast fund of tax money to the U.S. In the following exclusive review of the policies he has followed during his years with IRS, Mr. Caplin shows his complete understanding of the basic problems of the tax practitioner in his dealings with the Revenue Service.