Hard exclusive reactions and the two-gluon components of eta and eta' mesons

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.