This thesis explores global, or whole-field, optical diagnostics for combustion and related flow applications. Global optical diagnostics are becoming increasingly popular as an efficient way of measuring an entire flow field at one time. Conventional mechanical and optical point measurement techniques are first discussed and their limitations described. A variety of global optical diagnostics for visualisation, anemometry and film thickness measurement are then assessed. A summary of light scattering from particles is included, together with their behaviour when present in a flow. Suitable lasers and cameras for global diagnostics are also discussed. A family of global techniques have been reviewed in this thesis. Examples are presented to illustrate the strengths and limitations which make different techniques appropriate for different types of flow. A detailed description of a particle image velocimetry (PIV) system has been made. An example application is presented, showing how it can be used to aid the study of a simulated IC engine block flow. A comparison of the PIV data with laser Doppler anemometry data and computational fluid dynamics data is then made. Global optical techniques are then applied to two combustion applications; diesel fuel sprays and pulverised coal furnaces. Laser sheet illumination is applied to semi-industrial scale coal furnaces for what is believed to be the first time. Development of the techniques and optimisations made to them for these applications are described. Finally the current experimental challenges and future application of global optical diagnostics have been reviewed.