  We review some aspects of the quantum Yangians as symmetry algebras of
two-dimensional quantum field theories. The plan of these notes is the
following: 1 - The classical Heisenberg model: Non-Abelian symmetries;
  The generators of the symmetries and the semi-classical Yangians;
  An alternative presentation of the semi-classical Yangians;
  Digression on Poisson-Lie groups. 2 - The quantum Heisenberg chain:
  Non-Abelian symmetries and the quantum Yangians;
  The transfer matrix and an alternative presentation of the Yangians;
  Digression on the double Yangians. Talk given at the "Integrable Quantum
Field Theories" conference held at Come, Italy , September 13-19, 1992.
