A　catalytic　trifluoromethylselenolation　of　aryl　and　alkyl　halides　by　a　Cu(I)　catalyst　has　been　developed.　A　key　intermediate,　[(phen)Cu(SeCF3)](2)　(5)　was　successfully　isolated　and　characterized　by　X-ray　diffraction.　The　important　role　of　silver　in　the　transmetalation　process　during　the　catalytic　cycle　was　elucidated.　A　wide　range　of　trifluoromethylselanes　have　been　prepared　from　readily　available　starting　materials　from　a　method　that　tolerates　various　important　functional　groups.