We construct a bordification of Outer Space analogous to the Borel-Serre bordification of symmetric spaces. As an application,
we show that
Out(F
n
) is (2
n-5)-connected at infinity and that it is a virtual duality group of dimension 2
n-3.
Oblatum 4-III-1998 & 2-XII-1999¶Published online: 21 February 2000