  We critically reexamine the formalism for treating the leading-twist
contributions from the two-gluon Fock components occurring in hard processes
that involve eta and eta' mesons and establish a consistent set of conventions
for the definition of the gluon distribution amplitudes, the anomalous
dimensions as well as the projector of a two-gluon state onto an eta or eta'
state. We calculate the eta, eta'--photon transition form factor to order
alpha_s and show the cancellation of the collinear and UV singularities
explicitly. An estimate of the lowest Gegenbauer coefficients of the gluon and
quark distribution amplitudes is obtained from a fit to the eta, eta'--photon
transition form factor data. In order to elucidate the role of the two-gluon
Fock component further, we analyze electroproduction of eta, eta' mesons and
the g*g* eta (eta') vertex.
