Via building computational (typically mathematical and computer simulation) 
models, human performance modeling (HPM) quantifies, predicts, and maximizes 
human performance, human-machine system productivity and safety. This paper 
describes and summarizes the five key questions of human performance modeling: 
1) Why we build models of human performance; 2) What the expectations of a good 
human performance model are; 3) What the procedures and requirements in building 
and verifying a human performance model are; 4) How we integrate a human 
performance model with system design; and 5) What the possible future directions 
of human performance modeling research are. Recent and classic HPM findings are 
addressed in the five questions to provide new thinking in HPM's motivations, 
expectations, procedures, system integration and future directions.