  We introduce a set of gauge invariant fermion fields in fermionic coset
models and show that they play a very central role in the description of
several Conformal Field Theories (CFT's). In particular we discuss the explicit
realization of primaries and their OPE in unitary minimal models, parafermion
fields in $Z_k$ CFT's and that of spinon fields in $SU(N)_k, k=1$
Wess-Zumino-Witten models (WZW) theories. The higher level case ($k>1$) will be
briefly discussed. Possible applications to QHE systems and spin-ladder systems
are addressed.
