This progress report outlines the main principles for the development of a simple conceptual rainfall-runoff model at the Swedish Meteorological and Hydrological Institute. The HBV-2 Model is based on lumped-parameter approximations to the physical laws governing infiltration, percolation and runoff formation. The time interval is one day. The model structure includes a soil moisture storage, an upper zone storage and a lower zone storage. A procedure for evaluating the parameter values is described. Examples of applications to several test catchments in various hydrologic settings are included.