Combinatorial Group Theory lives in the fertile region between pure group theory and pure topology. The interplay between the logical
precision of algebra and the intuitive depths of geometry gives it charm and
strength. Lyndon suggests in his article that perhaps there is no exact
definition of the subject. Certainly it includes the study of equations
over groups (which tends to involve the study of geometric diagrams),
much of 3-manifold theory (the Poincare Conjecture is equivalent to a
group-theoretic question), group actions on geometric-combinatorial
objects such as trees, the theory of surface automorphisms, and many
other developments. As the Walrus said, the time has come to talk of
many things.