The study and exploitation of connections between group theory and geometry
has a long and glorious history. It also forms one of the main areas of ma
thematical research at the present day. This particular chapter in that sto
ry began in 1968 with seminal work of Milnor relating the curvature of a di
fferentiable manifold to the rate of growth of its fundamental group. This
article contains a brief survey of developments in the subject since that t
ime.