  The Baryon-Lepton difference ($B-L$) is increasingly emerging as a possible
new symmetry of the weak interactions of quarks and leptons as a way to
understand the small neutrino masses. There is the possibility that current and
future searches at colliders and in low energy rare processes may provide
evidence for this symmetry. This paper provides a brief overview of the early
developments that led to B-L as a possible symmetry beyond the standard model,
and also discusses some recent developments.
