Magnetostatics of thin wires is a specific branch of theoretical physics. Its main equation always contains a source, which can only be an endless curve in form. The field of an arc, which has endpoints, is not defined, therefore, there exists only entire field of an entire endless wire. This feature of the subject does not allow to employ the method of Green's functions, which requires that a wire is divided into small pieces. Therefore, only entire filed of an endless wire exists, therefore, such a wire plays the role of the "elementary" source. In this book an approach is outlined, which allows to construct magnetic fields of a quite broad variety of curves.