A review of the transient liquid phase (TLP) bonding process is presented in this paper. This review concentrates on the mechanisms of the TLP process, including both microstructural development and wettability aspects. However, design related issues and engineering applications are also considered. The paper explains how the TLP bonding process offers the potential for producing joints with microstructures and hence mechanical properties that are similar to those of the parent materials. The process of isothermal solidification is discussed at some length. The paper considers the ways in which specific microstructural features of the substrate material-interlayer material combination influence microstructural development. A distinction is drawn between cases where the progression of isothermal solidification dominates the final microstructure and those where events occurring after the completion of isothermal solidification are paramount. The paper describes the practical limitations on the production of parent-metal-like microstructures and the complexity of microstructural development in real materials, especially where dissimilar substrates are involved. Modification of the TLP bonding process to accommodate cases of limited solid solubility and/or low diffusion coefficients is discussed. STWJ/447