A review is presented of recent results obtained at Imperial College, London on two-phase gas-liquid slug flow in horizontal pipes. The survey begins by reviewing work on the mechanism for transition between stratified flow and slug flow. Correlations for slug frequency are then discussed. Next, models for prediction of slug creation and evolution are reviewed; it is shown that slug formation is a complex process, occurring at various distances from the entrance. The application of one-dimensional two-fluid models to the prediction of slug formation and evolution is discussed and their limitations reviewed. Experimental and CFD studies of slug tail and slug front behaviour are then described and Ute inclusion of the results of this work into an overall slug evolution model is discussed. Finally, transients involving slug flow are reviewed and exemplified by a transient in which the gas flow is reduced (a “down-gas” transient). Predictions of such a transient using a commercial two-fluid model code are used to illustrate the difficulties that can be encountered in such predictions.