The main ways of improving the compatibility of The main ways of improving the compatibility of polymer ± polymer compositions containing polyolefins as one polymer ± polymer compositions containing polyolefins as one component are considered. Considerable attention is given to the component are considered. Considerable attention is given to the preparation of polyolefins in the presence of an ingredient bound preparation of polyolefins in the presence of an ingredient bound to the catalyst in the catalytic (including consecutive) polymer-to the catalyst in the catalytic (including consecutive) polymerisation of olefins. The so-called reactor blends and the synthesis isation of olefins. The so-called reactor blends and the synthesis and structure of diblock and conducting composites are described. and structure of diblock and conducting composites are described. The important role of compatibilisation of polymers of different The important role of compatibilisation of polymers of different nature with the use of a third component is pointed out. The nature with the use of a third component is pointed out. The formation mechanism of molecular compositions, the structure formation mechanism of molecular compositions, the structure and properties of the intermediate layer and the main fields of and properties of the intermediate layer and the main fields of application of synthetic polyolefin ± polymer compositions are application of synthetic polyolefin ± polymer compositions are discussed. The bibliography includes 335 references discussed. The bibliography includes 335 references. .