  Let $n$ be a non-negative integer. Combining algebraic and combinatorial
techniques, we investigate for which pairs $(G,\rho)$ of a subgroup $G$ of the
symmetric group $S_n$ and an irreducible character $\rho$ of $G$ the induced
character $\rho\!\uparrow^{S_n}$ is multiplicity-free. As a result, for $n\geq
66$, we classify all subgroups $G\leq S_n$ which give rise to such a pair.
Moreover, for the majority of these groups $G$ we identify all the possible
choices of the irreducible character $\rho$, assuming $n\geq 73$.
