Among the most suggestive observations in soil research is the realisation that certain organic materials decompose slower than others, and a long tradition calls those organic materials that are decomposing slowly "recalcitrant" or "stable". Contemporary thinking, represented by the carbon-quality temperature (CQT) theory, assigns greater temperature sensitivity to the decomposition of such organic materials that are more "recalcitrant". But there is debate about whether it is conceptually appropriate to explain slow decomposition as a result of material properties of the organic matter, i.e. the inherent ability of certain organic materials to resist the attack of the decomposers, or whether it is mechanistically more accurate to interpret variations in decomposition rate as the consequence of the logistic and environmental constraints which act on the decomposer community and dictate substrate preferences and resource availability. 

In this contribution I review and examine the role of molecular structure (aka "soil organic matter quality" or "inherent recalcitrance") for soil organic matter decomposition. I will attempt to provide answers to the questions: How does molecular structure of soil organic matter factor in the complex chain of events that convert reduced soil carbon to CO2? and: How important is perceived "recalcitrance" of organic carbon for the temperature sensitivity of soil organic matter decomposition ?