Theoretical Aspects of Topologically Unquenched QCD

I give an outline of my proposal to take the QCD functional determinant in lattice simulations partially into account: The determinant is split into two factors, the factor referring to a standard background in each topological sector is kept exactly, the factor describing the effect of the smooth deviation of the actual configuration from the reference background is replaced by one. The issue of how to choose the reference configurations is discussed and it is argued that ``topologically unquenched QCD'' is an interesting starting point to study full QCD in lattice simulations as it gets the main qualitative features right from the beginning.