  The low-energy and low-momentum dynamics of systems with a spontaneously
broken continuous symmetry is dominated by the ensuing Nambu-Goldstone bosons.
It can be conveniently encoded in a model-independent effective field theory
whose structure is fixed by symmetry up to a set of effective coupling
constants. We construct the most general effective Lagrangian for the
Nambu-Goldstone bosons of spontaneously broken global internal symmetry up to
the fourth order in derivatives. Rotational invariance and spatial
dimensionality of one, two or three are assumed in order to obtain compact
explicit expressions, but our method is completely general and can be applied
without modifications to condensed matter systems with a discrete space group
as well as to higher-dimensional theories. The general low-energy effective
Lagrangian for relativistic systems follows as a special case. We also discuss
the effects of explicit symmetry breaking and classify the corresponding terms
in the Lagrangian. Diverse examples are worked out in order to make the results
accessible to a wide theoretical physics community.
