Several studies have shown that metastatic cancer cells may lie dormant in a secondary site for more than a decade, all the while retaining the ability to aggressively reemerge. Once these dormant cancer cells regrow, cancer becomes incurable, yet the mechanisms that instruct metastatic cancer cells to become dormant and later escape from dormancy still remain unknown. In this review we will discuss the known regulatory roles of the microenvironment in tumour dormancy and some potential models for future studies of tumour dormancy. Better understanding of the mechanisms involved has the potential to lead to significant improvements in the care of advanced cancer patients and the prevention of cancer recurrence.