<p>We prove that every nonassociative Novikov algebra can be equipped with a nontrivial structure of a Novikov–Poisson algebra. Using this result, we show that, under certain finiteness conditions, every simple Novikov algebra is obtained by the Gelfand–Dorfman construction applied to an associative commutative differentially simple algebra. We also introduce and study the Witt doubles of Novikov–Poisson algebras. The description of the isomorphisms of simple Novikov algebras over an algebraically closed field is reduced to the description of some special automorphisms of the underlying associative commutative algebras.</p>