Graphene nanoribbons—narrow strips of sp2-bonded carbon atoms—are considered highly promising candidates for post-silicon electronics due to their diverse electronic properties. In this Thesis, I present a series of studies aimed at both elucidating established electronic properties of graphene nanoribbons and exploring novel ways to engineer new functionalities in these nanostructures. Specifically, I demonstrate that the semiconducting nature of armchair-edged graphene nanoribbons is governed by a hidden symmetry intrinsic to their crystal structure at certain widths. Furthermore, I show that the application of a transverse electric field to armchair-edged graphene nanoribbons induces a semiconductor-to-semimetal transition, leading to the emergence of Dirac points at the Fermi level. Next, I investigate the electronic properties of zigzag-edged graphene nanoribbons embedded in hexagonal boron nitride, revealing that these heterojunctions exhibit half-semimetallic behavior: they conduct for electrons of one spin while remaining insulating for electrons of the opposite spin. Finally, I explore the electronic and optical properties of graphene nanostrips with Möbius geometry, showing that these nanostructures are chiral and feature strong optical activity. Overall, the findings presented in this Thesis provide new insights into graphene nanoribbons and lay the foundation for their future applications in nanoelectronics, spintronics, and photonics.