The existing derivations of a heavy quark effective theory (HQET) are
presented from a unified point of view. It is shown that a correct nor
malization of the heavy quark field in the effective theory is crucial
for making explicit the mass dependence of the matrix elements. A pos
sible variant of HQET which satisfies this requirement and which is co
nstructed from a sequence of Foldy-Wouthuysen transformations is prese
nted. The renormalization of the resulting effective Lagrangian to ord
er 1/m(2) is performed including also effects arising from vacuum pola
rization.