Over the last decade, the concept of stone decay being caused solely by one or two processes has been revised in favour of a more holistic notion that many operate together, are synergistic and possibly cyclical or seasonal. Certain of these processes may become predominant over others at particular times of the year or at specific periods in the history of the stone. Many researchers from different disciplines now agree that biological deterioration is of significance, and cross disciplinary work is becoming the rule rather than the exception. This short introduction gives an overall view of the principal mechanisms important in stone biodeterioration. The main groups of micro-organisms found on stone and their role in stone biodeterioration are reviewed. The final section discusses decay processes which can be brought about by many different groups of micro-organisms living together as a complex microbial community at the stone surface.