  Parton convolution models have been used extensively in describing the sea
quarks in the nucleon and explaining quark distributions in nuclei (the EMC
effect). From effective field theory point of view, we construct the parton
convolution formalism which has been the underlying conception of all
convolution models. We explain the significance of scheme and scale dependence
of the auxiliary quantities such as the pion distributions in a nucleon. As an
application, we calculate the complete leading nonanalytic chiral contribution
to the isovector component of the nucleon sea.
