Fluidized bed combustion (FBC) has the considerable advantage of being capable of burning high-sulphur fuels while achieving in situ sulphur capture by means of limestone addition. Unfortunately the efficiency of this process is limited, and limestone utilization in the range of 30-45% is not uncommon. In consequence, improving limestone utilization has long been an aim of FBC research. The principal directions this research has taken are the use of water (as liquid or vapour) to reactivate the spent sorbent, or mixing of chemical additives with the limestone to improve its utilization. Despite research stretching over the entire history of FBC combustion, there are still no working commercial applications of reactivation technology noted in the open literature. It is the aim of this paper to present some of the more important research undertaken in this field and to explore the major knowledge gaps that still exist in the area of sorbent reactivation. (c) 2006 Elsevier Ltd. All rights reserved.