  We study the correlation functions of logarithmic conformal field theories.
First, assuming conformal invariance, we explicitly calculate two-- and three--
point functions. This calculation is done for the general case of more than one
logarithmic field in a block, and more than one set of logarithmic fields. Then
we show that one can regard the logarithmic field as a formal derivative of the
ordinary field with respect to its conformal weight. This enables one to
calculate any $n$-- point function containing the logarithmic field in terms of
ordinary $n$--point functions. At last, we calculate the operator product
expansion (OPE) coefficients of a logarithmic conformal field theory, and show
that these can be obtained from the corresponding coefficients of ordinary
conformal theory by a simple derivation.
