  We present a computation of B-meson decay constants from lattice QCD
simulations within the framework of Heavy Quark Effective Theory for the
b-quark. The next-to-leading order corrections in the HQET expansion are
included non-perturbatively. Based on Nf=2 gauge field ensembles, covering
three lattice spacings a (0.08-0.05)fm and pion masses down to 190MeV, a
variational method for extracting hadronic matrix elements is used to keep
systematic errors under control. In addition we perform a careful
autocorrelation analysis in the extrapolation to the continuum and to the
physical pion mass limits. Our final results read fB=186(13)MeV, fBs=224(14)MeV
and fBs/fB=1.203(65). A comparison with other results in the literature does
not reveal a dependence on the number of dynamical quarks, and effects from
truncating HQET appear to be negligible.
