  A perfect code in a graph $\Gamma = (V, E)$ is a subset $C$ of $V$ such that
no two vertices in $C$ are adjacent and every vertex in $V \setminus C$ is
adjacent to exactly one vertex in $C$. A subgroup $H$ of a group $G$ is called
a subgroup perfect code of $G$ if there exists a Cayley graph of $G$ which
admits $H$ as a perfect code. Equivalently, $H$ is a subgroup perfect code of
$G$ if there exists an inverse-closed subset $A$ of $G$ containing the identity
element such that $(A, H)$ is a tiling of $G$ in the sense that every element
of $G$ can be uniquely expressed as the product of an element of $A$ and an
element of $H$. In this paper we obtain multiple results on subgroup perfect
codes of finite groups, including a few necessary and sufficient conditions for
a subgroup of a finite group to be a subgroup perfect code, a few results
involving $2$-subgroups in the study of subgroup perfect codes, and several
results on subgroup perfect codes of metabelian groups, generalized dihedral
groups, nilpotent groups and $2$-groups.
