  We consider use of collective variables for description of composite fields
as collective phenomena due to the strong coupling regime. We discuss two
approaches, where identification of collective variables of complex quantum
system does not depend on knowledge of other degrees of freedom: (a) collective
variables as parameters of group transformations changing the path integral of
the system, and (b) collective variables as background fields for quantum
system. In the case (a) we briefly present an approach. In the case (b) we
consider fermions in an external scalar field, which serves as a collective
variable in a nonlinear model for composite scalar field with a finite
compositeness scale.
