**Abstract**

With the rising emphasis on efficient and highly selective chemical transformations, the field of ruthenium-catalysed hydrogenation and hydrogenolysis reactions has grown tremendously over recent years. The advances are triggered by the detailed understanding of the catalytic pathways that have enabled researchers to improve known transformations and realise new transformations in biomass conversion. Starting with the properties of ruthenium, this chapter introduces the concept of the catalytic function as a basis for rational design of ruthenium catalysts. Emphasis is placed on discussing the principles of dissociative adsorption of hydrogen. The principles are then applied to the conversion of typical biomolecules such as cellulose, hemicellulose and lignin. Characteristic features make ruthenium catalysis one of the most outstanding tools for implementing sustainable chemical transformations.

**Keywords:** ruthenium, catalysis, reaction network, sequential reactions, hydrogen dissociation, hydrogenation, hydrogenolysis, biomass conversion
