  The aim of the present article is to study in detail the so-called spin
equation (SE) and present both the methods of generating new solution and a new
set of exact solutions. We recall that the SE with a real external field can be
treated as a reduction of the Pauli equation to the (0+1)-dimensional case.
Two-level systems can be described by an SE with a particular form of the
external field. In this article, we also consider associated equations that are
equivalent or (in one way or another) related to the SE. We describe the
general solution of the SE and solve the inverse problem for this equation. We
construct the evolution operator for the SE and consider methods of generating
new sets of exact solutions. Finally, we find a new set of exact solutions of
the SE.
