  The perturbative QCD predictions concerning deep inelastic scattering at low
$x$ are summarized. The theoretical framework based on the leading log $1/x$
resummation and $k_t$ factorization theorem is described. The role of studying
final states in deep inelastic scattering for revealing the details of the
underlying dynamics at low $x$ is emphasised and some dedicated measurements,
like deep inelastic scattering accompanied by an energetic jet, the measurement
of the transverse energy flow and deep inelastic diffraction, are briefly
discussed.
