The Eighth Symposium on the Study of the Earth's Deep Interior (SEDI) was held at Garmisch-Partenkirchen, Germany, in the Bavarian Alps, from 4 to 9 July 2004. The meeting attracted about 150 participants to a varied program that expanded the range of topics from previous meetings, with somewhat more emphasis on the mantle, in addition to mantle–core interaction, and core studies. On this occasion attention was also turned to the deep interior of other planets as well as the Earth.

To decipher the internal structure and dynamics of the Earth and other planets, remote sensing is required, as the depths of planetary interiors remain inaccessible to our laboratories. Subsequently, predictive tools play a key role in interpreting such data. The Eighth SEDI came at a time following (and during) significant expansions in data quantity and/or quality in the geophysical sciences community. This added to the excitement in the air at the conference, as we are in a period of witnessing increasing documentation of how the dominant depth shells within Earth, for example, likely play important roles in planet-wide processes, i.e., the whole Earth thermal, chemical, and dynamical system, e.g., see Fig. 1.

The great benefit of SEDI meetings is to bring together expertise from a range of different disciplines that bear on illumination of Earth (and planetary) interiors, and to foster interaction and understanding of the information provided by different disciplines. In many cases, the multidisciplinary nature of Earth and planetary interior investigation is pivotal to facilitating discovery, as well as minimizing the often significant uncertainties.

The 2004 Symposium covered a broad range of topics with sessions on
(1) Physical properties of Earth materials.
(2) Earth's magnetic field: constraints on deep processes.
(3) Core dynamics and the geodynamo.
(4) Structure and interactions in the system inner core, outer core and mantle.
(5) Interaction of plate tectonics and deep mantle processes.
(6) High resolution images of the Earth's interior.
(7) Physical and chemical discontinuities and reservoirs in the Earth's mantle.
(8) Deep interiors of other planets.

Each session had a limited number of invited papers, accompanied by contributed papers which were discussed in lively poster sessions, with a directed discussion session to finish. This format led to extensive interaction between the participants over the entire meeting and good cross-linking between topics to provide an inter-disciplinary perspective on the interior of the Earth (and other planets).

We are fortunate that now there is a wealth of high quality seismological data and a good historical database for magnetic studies that provide greatly improved constraints on structure just above and within the Earth’s core. Computer modelling, with cluster computers, has reached the point where Earth-like regimes are accessible for convection and crystal properties in the mantle and core. The complexities of the fluid and electromagnetic interactions in the dynamo action of the core are also being tackled with physical models; two different approaches are represented among the papers collected here.

The papers appearing in this special issue provide a good reflection of the breadth of studies of the Earth's deep interior. Although there is a concentration of attention on problems relating to the nature of the lowermost mantle and core, we also include general mantle convection issues and the properties of the moon.