  We construct the crystalline fundamental group of a semi-stable variety over
a field of positive characteristic using the log De Rham-Witt complex and
Navarro-Aznar's derived Thom-Whitney functor. This approach gives a relatively
direct comparison theorem with the De Rham fundamental group in the liftable
case. Also, we get a natural weight filtration which makes the coordinate ring
of the crystalline fundamental group into a mixed isocrystal when the variety
is defined over a finite field. Finally, the monodromy operator on the
crystalline fundamental group is used to prove a crystalline analogue of Oda's
good reduction criterion for curves.
