Discussion of the designation of multiple-star components leads to a conclusion that, apart from components, we need to designate systems and centers-of-mass. The hierarchy is coded then by simple links to parent. This system is adopted in the multiple star catalogue, now available on-line. A short review of multiple-star statistics is given: the frequency of different multiplicities in the field, periods of spectroscopic sub-systems, relative orbit orientation, empirical stability criterion, and period-period diagram with its possible connection to formation of multiple stars.

6 pages, 4 figures. To be published in the Proceedings of the ESO Workshop "Multiple stars across the HR diagram", Garching, July 12-15, 2005