In this article, we describe our chemical approach, developed over the course of a decade, towards the bottom‐up synthesis of structurally well‐defined graphene nanoribbons (GNRs). GNR synthesis can be achieved through two different methods, one being a solution‐phase process based on conventional organic chemistry and the other invoking surface‐assisted fabrication, employing modern physics methodologies. In both methods, rationally designed monomers are polymerized to form non‐planar polyphenylene precursors, which are “graphitized” and “planarized” by solution‐mediated or surface‐assisted cyclodehydrogenation. Through these methods, a variety of GNRs have been synthesized with different widths, lengths, edge structures, and degrees of heteroatom doping, featuring varying (opto)electronic properties. The ability to chemically tailor GNRs with tuned properties in a well‐defined manner will contribute to the elucidation of the fundamental physics of GNRs, as well as pave the way for the development of GNR‐based nanoelectronics and optoelectronics. Fabrication of chemically precise graphene nanoribbons (GNRs) has been achieved based on bottom‐up syntheses from small oligophenylene precursors. The GNR synthesis can be carried out through two different methods: a conventional solution synthesis and an on‐surface fabrication under ultrahigh vacuum conditions. In both methods, carefully designed monomers are polymerized to non‐planar polyphenylene precursors, which are “graphitized” and “planarized” by solution‐mediated or surface‐assisted cyclodehydrogenation. Through these protocols we have successfully prepared a number of GNRs with different widths and lengths, edge structures, and heteroatom doping, demonstrating tailor‐made (opto)electronic properties.