Massive stars are those with initial masses on the main sequence above about 8 solar masses, leading to core-collapse (or pair-instability) supernovae. They dominate the ecology of the Universe as "cosmic engines" via their extreme output in radiation and particles - not only as supernovae, but also during their entire lifetimes - with far-reaching consequences.

Although the existence of magnetic fields in massive stars is no longer in question, our knowledge of the basic statistical properties of massive star magnetic fields is seriously incomplete. There is a troubling deficit in our knowledge of the scope of the influence of fields on massive star evolution, and almost no empirical basis for how fields modify mass loss. The MiMeS project represents a consensus effort by an international team of recognized researchers who have compiled a strategic sample of sources to address these outstanding issues.