  I describe recent developments in quenched chiral perturbation theory (QChPT)
and the status of weak matrix elements involving light quarks. I illustrate
how, with improved statistical errors, and with calculations of the masses of
baryons containing non-degenerate quarks, there is now a clear need for
extrapolations of higher order than linear in the quark mass. I describe how
QChPT makes predictions for the functional forms to use in such extrapolations,
and emphasize the distinction between contributions coming from chiral loops
which are similar to those present in unquenched theories, and those from
$\eta'$ loops which are pure quenched artifacts. I describe a fit to the baryon
masses using the predictions of QChPT. I give a status report on the numerical
evidence for $\eta'$ loops, concluding that they are likely present, and are
characterized by a coupling $\delta=0.1-0.2$. I use the difference between
chiral loops in QCD and quenched QCD to estimate the quenching errors in a
variety of quantities. I then turn to results for matrix elements, largely from
quenched simulations. Results for quenched decay constants cannot yet be
reliably extrapolated to the continuum limit. By contrast, new results for
$B_K$ suggest a continuum, ``quenched'' value of $B_K(NDR, 2 GeV) = 0.5977 \pm
0.0064 \pm 0.0166$, based on a quadratic extrapolation in $a$. The theoretical
basis for using a quadratic extrapolation has been confirmed. For the first
time there is significant evidence that unquenching changes $B_K$, and my
estimate for the value in QCD is $B_K(NDR, 2 GeV) = 0.66 \pm 0.02 \pm 0.11$.
Here the second error is a conservative estimate of the systematic error due to
uncertainties in the effect of quenching. A less conservative viewpoint reduces
$0.11$ to $0.03$.
