  We define Anderson-Brown-Cisinski (ABC) cofibration categories, and construct
homotopy colimits of diagrams of objects in ABC cofibration categories.
Homotopy colimits for Quillen model categories are obtained as a particular
case. We attach to each ABC cofibration category a left Heller derivator. A
dual theory is developed for homotopy limits in ABC fibration categories and
for right Heller derivators. These constructions provide a natural framework
for 'doing homotopy theory' in ABC (co)fibration categories.
