  Anomalies are a very powerful tool in constraining theories beyond the
standard model. We give a pedagogical overview of some topics illustrating the
important role played by spacetime anomalies in string theory. After discussing
the general problem of anomaly cancellation in quantum field theory, the focus
is set on the cancellation of anomalies in type-I string theory through the
Green-Schwarz mechanism. The notion of anomaly inflow is also reviewed, as well
as its application to the evaluation of D-brane anomalous couplings. Finally,
we briefly comment on recent developments concerning the reformulation of
anomalies in the language of category theory.
