Multiplicity of charged particles in relativistic heavy-ion interactions

The importance of the charged-particle multiplicity measurement in hadron interactions for understanding of the production mechanism at work is outlined. This subject has received a new interest since the measurements by the experiments at RHIC, being related to the estimation of particle densities foreseen in ALICE. A general overview of the present status, including the findings of the experiments at SPS and the implications for the QGP phase transition is presented.