  Graphene nanoribbons (GNRs) are one-dimensional nanostructures predicted to
display a rich variety of electronic behaviors. Depending on their structure,
GNRs realize metallic and semiconducting electronic structures with band gaps
that can be tuned across broad ranges. Certain GNRs also exhibit a peculiar
gapped magnetic phase for which the half-metallic state can be induced as well
as the topologically non-trivial quantum spin Hall electronic phase. Because
their electronic properties are highly tunable, GNRs have quickly become a
popular subject of research toward the design of graphene-based nanostructures
for technological applications. This Account presents a pedagogical overview of
the various degrees of freedom in the atomic structure and interactions that
researchers can use to tailor the electronic structure of these materials. The
Account provides a broad picture of relevant physical concepts that would
facilitate the rational design of GNRs with desired electronic properties
through synthetic techniques.
