  We present here an overview of our work concerning entanglement properties of
composite quantum systems. The characterization of entanglement, i.e. the
possibility to assert if a given quantum state is entangled with others and how
much entangled it is, remains one of the most fundamental open questions in
quantum information theory. We discuss our recent results related to the
problem of separability and distillability for distinguishable particles,
employing the tool of witness operators. Finally, we also state our results
concerning quantum correlations for indistinguishable particles.
