[en] To the method of boundary integral equations (BIE method) the paper attributes each method of solution of boundary-value problems of neutron transport theory in media with cross-sections, piecewise-constant with respect to space coordinate provided the method is based on reduction of the boundary-value problem considered to the solution of respective BIEs. The paper gives the definition of these notions, considers basic schemes of the method as well as basic BIE types, including a new BIE type introduced in this paper