We study logarithmic conformal field theories (LCFTs) through the introduct
ion of nilpotent conformal weights. Using this device, we derive the proper
ties of LCFTs such as the transformation laws, singular vectors and the str
ucture of correlation functions. We discuss the emergence of an extra energ
y momentum tensor, which is the logarithmic partner of the energy momentum
tenser. (C) 2001 Elsevier Science B.V. All rights reserved.