This work covers homogeneous and biphasic catalysis in ionic liquids and water. The work presented herein is divided into two major parts: catalytic hydrogenation and catalytic hydroformylation. The first part also serves as an introduction to catalysis in ionic liquids and water in general. The hydrogen solubility in ionic liquids is determined, and the effect on hydrogenation turnover frequencies in the catalytic reduction of benzene to cyclohexane in ionic liquids studied. The ruthenium catalysed reduction of bicarbonate in ionic liquid-aqueous biphasic systems is investigated and the in situ identification of ruthenium species reported. Recycling of the catalyst was hampered by the formation of inactive ruthenium carbonyl species. Preliminary results in the reduction of maleic acid and 5-hexen-2-one under solvent-free conditions, in water and in the presence of ionic liquids are reported. Whereas the mechanism appears to be colloidal when the reduction is carried out neat and in the presence of ionic liquid, it may be homogeneous in water. The second part is concerned with hydroformylation in ionic liquids. The solubility of carbon monoxide has been determined in a considerable number of ionic liquids, and the influence of the anion and cation on the solubility studied. The influence was found to be greater than for dihydrogen. The results were correlated with rhodium catalysed hydroformylation in ionic liquids. Finally, the development of a solvent-parameter scale for the prediction of solvent properties of ionic liquids is introduced. The approach was found to allow for the prediction of the carbon monoxide solubility in ionic liquids.