Multiple oxygenate groups in biomass-based feedstocks are open to multiple catalytic pathways and products, typically resulting in low selectivity for the desired products. In this context, strategies for rational catalyst design are critical to obtain high selectivity for the desired products in biomass upgrading. The Sabatier principle provides a conceptual framework for designing optimal catalysts by following the volcanic relationship between catalyst activity for a reaction and the binding strength of a substrate on a catalyst. The affinity descriptor of catalysts, which scales the interaction strength of the functional groups of substrates with catalysts, can potentially be developed to correlate with catalyst performance in reactions. Specifically, the oxygen affinity of catalysts, as a measure of the interaction strength between oxygenates and catalysts, can be applied to rationalize the oxygenate transformation and guide the rational design of efficient catalysts based on the Sabatier principle. This review highlights the fundamental basis and applications of affinity descriptors in catalysis, with a focus on the oxygen affinity of catalysts for the transformation of biomass-derived oxygenate compounds.