Entanglement is a nonclassical correlation of compound quantum systems. We derive Separability-Eigenvalue-Equations. The solution of these equations delivers all observables for the determination of entanglement. On the other hand, it delivers entanglement quasi-probabilities. We conclude from negativities of such distributions, that no classical statistics can describe the state under study. For the quantification of entanglement we compare different entanglement measures. We also consider different kinds of entanglement and the relation to nonclassicality.