  In this talk, I address the comparison between results from lattice QCD
computations and Chiral Perturbation Theory (ChPT). I briefly discuss how ChPT
can be adapted to the much-used quenched approximation and what it tells us
about the special role of the $\eta'$ in the quenched theory. I then review
lattice results for some quantities (the pion mass, pion scattering lengths and
the $K^+\to\pi^+\pi^0$ matrix element) and what quenched ChPT has to say about
them.
