  A numerical semigroup is a subset of N containing 0, closed under addition
and with finite complement in N. An important example of numerical semigroup is
given by the Weierstrass semigroup at one point of a curve. In the theory of
algebraic geometry codes, Weierstrass semigroups are crucial for defining
bounds on the minimum distance as well as for defining improvements on the
dimension of codes. We present these applications and some theoretical problems
related to classification, characterization and counting of numerical
semigroups.
