This article presents in detail those results in ferromagnetic domain theory that have been obtained recently and have not previously appeared in monographs or reviews. A significant part of the article is devoted to consideration of basic problems of the theory. A detailed description is given of those properties of the domain structure that are independent of the properties of the model. As concrete examples, the domain structures in uniaxial and cubic ferromagnets are considered. Experimental results are cited only by way of illustration. Some generally accepted ideas have proved wrong and are subjected to criticism in this article.