AbstractGiardia lamblia is a protozoan pathogen of the human small intestine. The life cycle of Giardia and its capacity to differentiate from a motile trophozoite into a dormant, water-resistant cyst, and vice versa, is crucial for its pathogenesis. Although the physiological signals leading to encystation and excystation are known, the intracellular signalling pathways are poorly understood. Several signalling proteins have been reported to be involved in Giardia differentiation, but none have been united in a pathway. In this chapter, we summarize the signalling molecules known to affect Giardia differentiation and discuss their possible cross-talk, based on their localization and expression, and with reference to the current literature on signal transduction in other cell types.