Microbiologically influenced corrosion (MIC) is one of a number of threats to the long-term integrity of nuclear waste containers. As such, the potential for, and extent of, MIC must be assessed and suitable models developed for predicting the long-term behaviour of the container. There are two broad approaches to assessing the threat posed by MIC; first, to determine whether the environment will support microbial activity and, if so, where and when it will occur, and second, to estimate the maximum amount of damage that could occur if microbial activity in the repository is possible.