  We present and discuss a formal approach for describing the quantum to
classical crossover based on the group-theoretic construction of generalized
coherent states. The method was originally introduced by L. Yaffe in 1982 for
tackling large-$N$ quantum field theories, and has been recently used for
studying open quantum systems whose environment, while becoming macroscopic,
may or may not display a classical behaviour. Referring to these recent
developments, in this paper we provide the essential elements of Yaffes's
approach in the framework of standard quantum mechanics, so as to clarify how
the approach can be used without referring to quantum field theory. Moreover,
we address the role played by a possible global symmetry in making the
large-$N$ limit of the original quantum theory to flow into a formally well
defined classical theory, and we specifically consider the quantum-to-classical
crossover of angular momentum. We also give details of a paradigmatic example,
namely that of $N$ free one-dimensional spinless particles. Finally, we discuss
upon the foundational requirement that any classical description should
ultimately be derived from an underlying quantum theory, that however is not,
and should never be confused with, the one obtained via some quantization
procedure of the classical description itself.
