Leaf litter decomposition in lowland tropical forests represents a significant flux of carbon (C) to the atmosphere, and is controlled by both extrinsic site conditions and intrinsic litter traits. However, there is a gap in the understanding about the relative importance of these two factors, and of the role of interactions between them. Global change drivers, such as mean annual precipitation (MAP) change and soil nitrogen (N) fertilisation by deposition, could affect both pathways simultaneously. In order to predict the response of the global C cycle to future change, a further understanding of such interactions is required, and is the focus of this thesis. Using a range of experimental factorial studies, in the field and laboratory, in mature tropical forests in Panama, the relative and interactive effects on decomposition of MAP, soil N and phosphorus (P) availability, litter species identity, and litter N and P status, were determined. Leaf litter species identity was a significant predictor of decomposition across the landscape, whilst soil C:N ratio was more important than MAP. Within species, elevated P concentration and decreased N:P ratio in litter was associated with decreased C mineralisation. Increased soil N availability altered microbial community composition, which increased decomposition of some leaf litter types. The results highlight litter traits as an important driver of decomposition via species identify and intra-species leaf litter chemistry. Also, the implications of decomposer activity and composition for decomposition will depend on litter traits. This thesis contributes valuable research evidence to augment current understanding of the importance of litter traits, and their interactions with decomposers, as a pathway through which global change drivers could affect the C cycle in tropical forests.