Buoyant diapirs or plume heads in the Earth's mantle are typically modelled as a solitary bodies, ascending vertically and uninfluenced by neighboring diapirs. However, laboratory experiments and basic theory suggest that two or more rising diapirs can become attracted to each other, thereby influencing their ascent trajectory such that they cluster and possibly coalesce. Clustering is controlled by the horizontal and vertical separation between diapirs, as well as their relative sizes. This phenomena has implications for the origins of large igneous provinces as well as the Earth's long-wavelength hotspot distribution.¿ 1997 American Geophysical Union