The work presented in this thesis focuses on ways to utilise lignin as a renewable chemical resource using ionic liquids. Throughout, an understanding of the microscopic interactions between lignin (or lignin model compounds) and the components of ionic liquids has been developed. Application of this understanding in efforts towards developing ionic liquid based methodologies to separate lignin from biomass, to cleave and functionalise lignin, as well as extracting these functionalised lignin fragments for later use in either research or industry, is described. A range of different ionic liquids containing cations and anions of varying coordination strength were examined for their abilities to dissolve lignin. It was found that at least a moderately coordinating anion was required for the dissolution of lignin (likely due to interactions introduced between the anion and the lignin) but that the solubility of lignin in the resultant mixtures was typically limited by viscosity. The coordinating strength of the anion required for dissolution was seen to be lower than that seen previously for cellulose. A correlation between the cationic structure of the ionic liquid and the solubility of lignin was also found; it was identified that an unhindered aromatic system was important for the dissolution of lignin. These results were supported with NMR spectroscopic studies that identified the key interactions between lignin and the ionic liquids. The reaction between hydrogen bromide and a range of lignin model compounds was also examined in an ionic liquid identified during the solubility studies. Cleavage of ethers typically found in lignin with hydrogen bromide occurred in the ionic liquid but such cleavage was dramatically slowed by the presence of water. Kinetic analyses across a range of different model compounds (incorporating functionalities common in lignin) indicated selectivity for different reactive sites, including different ether types in the same model compound; this selectivity is contributed to by both steric and electronic effects. The favoured locations for reaction were seen to be locations that could most efficiently stabilise a positive charge; given this it was proposed that a key feature in the solvent effects of ionic liquids on this process is their effect on the protonation of the starting material to give the reactive intermediate that subsequently undergoes nucleophilic attack.The reaction conditions used in the kinetic studies were examined for their effect on lignin itself. Analysis of extracts from the treated lignin gave a measure of the extent of fractionation and functionalisation under these conditions. A selection of ionic liquids were considered for their potential use to separate lignin mixtures after the treatments developed above. The ionic liquid systems chosen were seen to be either completely immiscible, completely miscible or to have miscibilities that varied with temperature. It was demonstrated that the miscibility profile could be tuned through variation of the cation of one of the ionic liquids. These mixtures were then examined for their ability to selectively partition a range of organic molecules in efforts to develop a system for the selective separation of fractionated compounds from a complex lignin mixture.