Nondeterminism is one of features separating "real" programs from specifications. It is quite common phenomenon. For example, many descriptions of algorithms, including the classical ones given in textbooks, are nondeterministic. In the lecture, it will be mentioned classes of algebras, most popular in specification of of nondeterministism. One of them is a class of multialgebras. This kind of models will be compared with others. Finally, some languages and logical calculi for specifications of multialgebras will be presented.