 The cluster ion spectrometry, CIS, experiment on the four cluster spacecraft measures the full three-dimensional ion distribution of major magnetospheric ions from thermal energies to about 40 kev slash E using two different instruments, a composition and distribution function analyzer, CIS1 slash codiff, and a hot ion analyzer, CIS2 slash HIA. The CIS instruments have two different sensitivities, and first tests were achieved from early September 2000 to mid-January 2001. The operation phase began on February 1, 2001, and the paper presents the high-level performances and capabilities of the instruments, showing good examples of data obtained in various regions such as the central plasma sheet, magnetopause crossings, magnetosheath, solar wind, cusp measurements, and auroral regions. The results show the tremendous interest of multi-spacecraft measurements with identical instruments and open a new area in magnetospheric and solar wind-magnetosphere interaction physics. This article was offered by H. Reem, C. O. Sten, J. M. Boscade, and others. We're article.tv, links in the description below.