The Hydrologic Ensemble Prediction Experiment (HEPEX; www.hepex.org) is establishing a seasonal streamflow forecasting intercomparison project (SSFIP), or test bed, with the goal of understanding the strengths and weaknesses of the various ensemble forecasting approaches being developed in forecasting centers around the globe. While some centers have produced forecasts for decades (e.g. Ensemble Streamflow Prediction - ESP - in the United States and elsewhere), recent years have seen the proliferation of new operational and experimental streamflow forecasting approaches. Forecasting centers invariably develop their own modelling approaches and, consequently, model validation and forecast verification strategies vary greatly. Thus it is difficult to assess whether the approaches employed in some centers offer more promise for development than others. This motivates us to establish a forecasting test bed to facilitate a diagnostic evaluation of a range of different streamflow forecasting approaches, and their components, over a common set of catchments, using a common set of forecast verification methods. Rather than prescribing a set of scientific questions from the outset, experiments are dictated by the basin “host” and notable differences in methods applied to each basin. The initial pilot of the testbed involved testing CSIRO and NCAR forecasts for the Murray River, Australia, and the Hungry Horse reservoir drainage area, USA. To support this CSIRO and NCAR have developed data and analysis tools, data standards and protocols to formalize the experiment. These include requirements for cross-validation, verification, reference climatologies, and common predictands. Additional catchments/approaches are in the process of being added to the test bed through the inclusion of new forecasting centers. This presentation describes the SSFIP experiments, pilot basin results and scientific findings to date