This work summarizes knowledge from experts and from empirical studies, providing guidelines that can be applied in fields such as economics, sociology, and psychology. It applies to problems such as those in finance (how much is this company worth?), marketing (will a new product be successful?), personnel (how can we identify the best job candidates?), and production (what level of inventories should be kept?). The 30 chapters cover all types of forecasting methods, including judgmental methods such as Delphi, role-playing, and intentions studies. Quantitative methods include econometric methods, expert systems, and extrapolation. Some methods, such as conjoint analysis, analogies, and rule-based forecasting, integrate quantitative and judgmental procedures. In each area, the authors identify what is known in the form of "if-then principles", and they summarize evidence on these principles.