  The formalism for treating the leading-twist contributions of the two-gluon
Fock components occurring in hard exclusive processes that involve eta and eta'
mesons is reviewed. The calculation of the eta, eta'--photon transition form
factor in next-to-leading order in alpha_s, as well as, the analysis of the g*
g* eta' vertex and the electro- and photoproduction of eta, eta' mesons are
presented. Applications of this formalism to other relevant quantities such as
glueballs are also discussed.
