  Building on reduction theorems and dimension bounds for symmetric groups
obtained in our earlier work, we classify the irreducible restrictions of
representations of the symmetric and alternating groups to proper subgroups.
Such classification is known when the characteristic of the ground field is
greater than $3$, but the small characteristics cases require a substantially
more delicate analysis and new ideas. Our results fit into the Aschbacher-Scott
program on maximal subgroups of finite classical groups.
