We explain a fundamental additivity theorem for Euler characteristics and g
eneralized trace maps in triangulated categories, The proof depends on a re
fined axiomatization of symmetric monoidal categories with a compatible tri
angulation. The refinement consists of several new axioms relating products
and distinguished triangles. The axioms hold in the examples and shed ligh
t on generalized homology and cohomology theories. (C) 2001 Academic Press.