  Expanded and updated version of a talk originally presented at ``IVth Int.
Symp. on Pion--Nucleon Physics and the Structure of the Nucleon'', Bad Honnef,
9--13 September 1991, originally published in $\pi N$ Newletter 6 (1992)
21--32.
  Table of contents:
  1. Introduction.
  2. $\sigma$--terms and ``measurements'' of the strange--quark scalar density
of the nucleon.
  3. Methods of extrapolation to $q^2 = t = \omega^2 = 0$: a subjective review:
  3.1. The ``improved'' Altarelli--Cabibbo--Maiani method.
  3.2. The Fubini--Furlan analysis of meson-nucleus scattering lengths.
  3.2. The ``unitarized'' version of the Cheng--Dashen theorem.
  4. Capabilities for a $\bar{K}N$--scattering experiment at DA$\Phi$NE.
  5. ``Envoi''.
