  Lattice QCD allows a first-principles study of QCD with the freedom to vary
the number and masses of the quarks. I present results on the flavour singlet
correlations (this illuminates OZI violating effects) for mesons. Concentrating
on the pseudoscalar mesons, the flavour singlet mass splitting ($\eta$, $\eta'$
mass splitting) appears naturally.
  I also present results on an investigation of decay constants for the $\eta$
and $\eta'$ ($f_{\eta}$) and discuss which quantities may be accessible in
future lattice studies.
  The Witten-Veneziano approach can also be explored by determining the
quenched topological susceptibility on a lattice.
