  Let $G$ be a group. An automorphism of $G$ is called intense if it sends each
subgroup of $G$ to a conjugate; the collection of such automorphisms is denoted
by $\mathrm{Int}(G)$. In the special case in which $p$ is a prime number and
$G$ is a finite $p$-group, one can show that $\mathrm{Int}(G)$ is the
semidirect product of a normal $p$-Sylow and a cyclic subgroup of order
dividing $p-1$. In this thesis we classify the finite $p$-groups whose groups
of intense automorphisms are not themselves $p$-groups. It emerges from our
investigation that the structure of such groups is almost completely determined
by their nilpotency class: for $p>3$, they share a quotient, growing with their
class, with a uniquely determined infinite $2$-generated pro-$p$ group.
