  We describe the phenomenon of dynamical gluon mass generation within the
massless bound-state formalism, which constitutes the general framework for the
systematic implementation of the Schwinger mechanism in non-Abelian gauge
theories. The main ingredient of this formalism is the dynamical formation of
bound states with vanishing mass, which gives rise to effective vertices
containing massless poles; these vertices, in turn, trigger the Schwinger
mechanism, and allow for the gauge-invariant generation of an effective gluon
mass. In this particular approach, the gluon mass is directly related to
quantities that are intrinsic to the bound-state formation itself, such as the
"transition amplitude" and the corresponding "bound-state wave-function".
Specifically, a set of powerful relations discussed in the text, allows one to
determine the dynamical evolution of the gluon mass through a Bethe-Salpeter
equation, which controls the dynamics of the relevant wave-function. In
addition, it is possible to demonstrate that the massless bound-state formalism
is equivalent to the standard approach based on Schwinger-Dyson equations, thus
establishing a formal connection between two different nonperturbative
formalisms.
