© 2012 Springer Science+Business Media Dordrecht. All rights are reserved. In the complex environments in which they live, bacteria and fungi are in frequent contact. This leads to interactions that may be transient and occasional or constant and co-evolved. Although there are many forms interactions could take, the focus on this chapter is on those mediated by secreted metabolites. Antibiosis is one such interaction and some classical as well as novel interactions mediated by antibiotics are discussed. More recently, the concept of signal-mediated interactions between bacteria and fungi has gained currency. Some, or perhaps many, bacteria and fungi have developed the capacity to take advantage of, and in some cases, to subvert, signalling pathways in other organisms. This is addressed, in particular, the example of signalling between Pseudomonas aeruginosa and Candida albicans.