Depending on how you define ‘agency’, I think that technically there are only 16, not 17 agencies….. This might just be semantics but I don’t regard the Office of the Director of National Intelligence as an intelligence agency per se…… its role is organize, coordinate and manage the efforts of the other agencies, and the person who heads up this office reports directly to the President. Anyway, this is why some reports said 3 while some said 4…. the 4th one being the Office of the DNI.