Hydraulic habitat simulation models were designed for the quantitative determination of environmental flows that consider the needs of aquatic fauna in rivers and streams. In the past 50 years, the modeling techniques were significantly developed, but expectations associated with model utility also increased. Nowadays, the tools are expected to be applicable across a range of spatial and temporal scales and to protect entire aquatic communities, while being inexpensive as well as easy to use in administrative and legal environments. Addressing these challenges is the focus of this volume. We invited papers that present recent developments in habitat modeling, supported by real life case studies. The submitted papers well represent the wide applicability of habitat simulation models, allowing us to address both ends of river management requirements: the ability to address very detailed site specific issues as well as the ability to address the coarse scale applications necessary in regional management.