  Evolution equations describe the effect of consecutively integrating out all
quantum fluctuations with momenta larger than some infrared cutoff scale k. We
develop a formalism for the introduction of collective degrees of freedom at
some intermediate scale and derive the corresponding evolution equations. This
allows to account for the appearance of bound states at some characteristic
length scale as, for example, the mesons in QCD. The vacuum properties,
including condensates of composite operators, can be directly infered from the
effective action for k->0. We compute in a simple QCD-motivated model with
four-quark interactions the chiral condensate \bar\psi\psi and the effective
action for pions including f_\pi. A full treatment of QCD along these lines
seems feasible but still requires substantial work. (5 figures available by
ordinary mail upon request)
