  We develop various complementary concepts and techniques for handling quantum
fluctuations of Goldstone bosons.We emphasise that one of the consequences of
the masslessness of Goldstone bosons is that the longitudinal fluctuations also
have a diverging susceptibility characterised by an anomalous dimension $(d-2)$
in space-time dimensions $2<d<4$.In $d=4$ these fluctuations diverge
logarithmically in the infrared region.We show the generality of this
phenomenon by providing three arguments based on i). Renormalization group
flows, ii). Ward identities, and iii). Schwinger-Dyson equations.We obtain an
explicit form for the generating functional of one-particle irreducible
vertices of the O(N) (non)--linear $\sigma$--models in the leading 1/N
approximation.We show that this incorporates all infrared behaviour correctly
both in linear and non-linear $\sigma$-- models. Our techniques provide an
alternative to chiral perturbation theory.Some consequences are discussed
briefly.
