  The process $K_{\ell3}$ is calculated to two-loop order ($p^6$) in Chiral
Perturbation Theory (ChPT) in the isospin conserved case. We present
expressions suitable for use with previous work in two-loop CHPT where the
order $p^4$ parameters ($L_i^r$) were determined from experiment.
  We point out that all the order $p^6$ parameters ($C_i^r$) that appear in the
value of $f_+(0)$ relevant for the determination of $|V_{us}|$ can be
determined from $K_{\ell3}$ measurements via the slope and the curvature of the
scalar form-factor. As a by product we update the value of the CKM matrix
element $| V_{us} |$.
