The use of computer simulations to gain deeper understanding of complex dynamic systems has become widely accepted across scientific disciplines. Yet, the precision of results obtained in "virtual worlds" may be deceptive when they replace rather than reflect reality. The scope of this edited volume hence reaches beyond identifying areas in which computer-based simulations allow for results otherwise not possible, to include an assessment of their opportunities and limitations. Reflecting the field's interdisciplinarity, contributions range from astronomy over theoretical biology to economics.