PoS(LATTICE 2008)278 B and D Meson Decay Constants C. Bernard, 1 C. DeTar, 2 M. Di Pierro, 3 A. X. El-Khadra, 4 R. T. Evans, 4 E. D. Freeland, 5 E. Gamiz, 4 S. A. Gottlieb, 6 U. M. Heller, 7 J. E. Hetrick, 8 A. S. Kronfeld, 9 J. Laiho, 1 , 9 L. Levkova, 2 P. B. Mackenzie * , 9 J. Simone, 9 R. Sugar, 10 D. Toussaint, 11 and R. S. Van de Water 9 1 Washington University, 2 University of Utah, 3 DePaul University, 4 University of Illinois, 5 The School of the Art Institute of Chicago, 6 Indiana University, 7 American Physical Society, 8 University of the Pacific, 9 Fermi National Accelerator Laboratory, 10 University of California, Santa Barbara, 11 University of Arizona E-mail: mackenzie@fnal.gov Fermilab Lattice and MILC Collaborations We present an update of our calculations of the decay constants of the D, D s , B, and B s mesons in unquenched 2 + 1 flavor QCD. We use the MILC library of improved staggered gauge ensembles at lattice spacings 0.09, 0.12, and 0.15 fm, clover heavy quarks with the Fermilab normalizations, and improved staggered light valence quarks. The XXVI International Symposium on Lattice Field Theory July 14-19 2008 Williamsburg, Virginia, USA * Speaker. c  Copyright owned by the author(s) under the terms of the Creative Commons Attribution-NonCommercial-ShareAlike Licence. http://pos.sissa.it/