The properties of the Earth's coupled magnetosphere–ionosphere system are dominated by its interaction with the solar–wind plasma, mediated by magnetic reconnection at the magnetopause interface. As a consequence, Earth's magnetospheric dynamics depend primarily on the concurrent orientation of the interplanetary magnetic field (IMF). We illustrate current understanding of the system through the results of a number of recent case studies and highlight the remaining issues. The discussion centres on flux–transfer events and substorms during intervals of southward IMF and magnetopause and tail processes during intervals of northward IMF. We emphasize the great diagnostic power of combined in situ and remote–sensing observations from space and on the ground. ; This paper was published as Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences, 2003, 361 (1802), pp. 113-126. It is available from http://rsta.royalsocietypublishing.org/content/361/1802/113. Doi: 10.1098/rsta.2002.1112 ; Metadata only entry