A method is presented for the projection of a superposition of Slater determinants on states with definite angular momentum. The method can be used in the configuration mixing method or in the generator coordinate method. It is based on a projection operator of the form e -iα Ĵze -ϑ Ĵ+e Ĵ-e -iγ Ĵz and its expectation value is expanded in powers of e- iαM1 e- iϑM2e- ϑM3. Expectation values of operators needed for the calculation of energies and transition amplitudes between states of definite angular momenta are calculable from systems of linear equations related to these expectation values. Detailed formulas for the calculation of energy levels and transition amplitudes are presented, and algorithms suitable for computer programs are discussed.