Abstract: The purpose of the PHOENIX project is to develop an integrated modeling framework allowing to describe, position and analyze various long-term population issues. A systems dynamic modeling approach is applied to describe the demographic transition as a composite of its underlying components: the epidemiological and fertility transitions. Future fertility behavior and mortality patterns in major world regions are explored under varying socio-economic and environmental conditions by making use of the computer simulation model, PHOENIX plus. The theoretical background and model documentation can be found in the book World Population in Transition (Hilderink, 2000).