  We discuss direct $CP$ violation in the standard model by giving a new
estimate of $\varepsilon'/\varepsilon$ in kaon decays. Our analysis is based on
the evaluation of the hadronic matrix elements of the \mbox{$\Delta S =1$}
effective quark lagrangian by means of the chiral quark model, with the
inclusion of meson one-loop renormalization and NLO Wilson coefficients. Our
estimate is fully consistent with the $\Delta I =1/2$ selection rule in $K\to
\pi\pi$ decays which is well reproduced within the same framework. By varying
all parameters in the allowed ranges and, in particular, taking the quark
condensate---which is the major source of uncertainty---between $(-200\ {\rm
MeV})^3$ and $(-280\ {\rm MeV})^3$ we find $$ -5.0 \times 10^{-3}\
<\varepsilon'/\varepsilon <\ 1.4 \times 10^{-3}\ .$$ Assuming for the quark
condensate the improved PCAC result \mbox{$\vev{\bar qq} = -(221\: \pm 17\ {\rm
MeV})^3$} and fixing $\Lambda_{\rm QCD}^{(4)}$ to its central value, we find
the more restrictive prediction $$\varepsilon '/\varepsilon = ( 4 \pm 5 )
\,\times \,10^{-4}\ , $$ where the central value is defined as the average over
the allowed values of Im $\lambda_t$ in the first and second quadrants. In
these estimates the relevant mixing parameter Im $\lambda_t$ is
self-consistently obtained from $\varepsilon$ and we take $m_t^{\rm pole} = 180
\pm 12$ GeV. Our result is, to a very good approximation, renormalization-scale
and $\gamma_5$-scheme independent.
