Solid waste landfills are an extremely complex and heterogeneous environment. Modeling the biodegradation processes within a landfill must involve an understanding of how environmental factors affect these processes. Arguably, the most important environmental factor influencing biodegradation processes is solid waste moisture content. This thesis effort, which is an extension of a system dynamics model previously presented by Colborn (1997) and amended by Benter (1999), attempts to understand and model the effects of moisture content on waste degradation and landfill gas generation. The new moisture structure that was added to the previous models provides a better representation of the impact of moisture on aerobic and anaerobic hydrolysis and bacterial populations, and ultimately, gas generation. It also gives a clearer picture of how moisture is distributed between the solid waste and the void spaces within a landfill. Leachate and moisture infiltration flows were introduced into the model as a means to replicate the "wet-cell" or bioreactor landfill.