  We present in this contribution the basic formul\ae\ for the analysis of
low--momentum charged-- and neutral--kaon interactions in hydrogen, including
as well a (brief) description of the problems left open by past experiments,
and of the improvements DA$\Phi$NE can be expected to offer over them.
Interactions in deuterium and other light nuclei will be only briefly
mentioned, and only in those respects touching directly upon the more
``elementary'' aspects of kaon--nucleon interactions.
