  I study the technique of Algebraic Bethe Ansatz for solving integrable models
and show how it works in detail on the simplest example of spin 1/2 XXX
magnetic chain. Several other models are treated more superficially, only the
specific details are given. Several parameters, appearing in these
generalizations: spin $s$, anisotropy parameter $\ga$, shift $\om$ in the
alternating chain, allow to include in our treatment most known examples of
soliton theory, including relativistic model of Quantum Field Theory.
