Nitrogen-doped graphene (N-G) has emerged as a structurally tunable and chemically versatile nanomaterial with exceptional potential for diverse electrochemical and electronic applications. This chapter provides a comprehensive overview of the physical and chemical structures of N-G, elucidating how nitrogen incorporation modifies the intrinsic properties of pristine graphene. The discussion begins with the fundamental aspects of graphene’s lattice and defect formation, followed by an exploration of how nitrogen doping, through substitutional or functional group incorporation, alters its morphology, electronic structure, and chemical reactivity. Exclusive studies have been conducted to the optimize of synthesis parameters on the structural and electronic configurations of N-G, as these determine the type and distribution of nitrogen functional groups such as graphitic-N, pyridinic-N, pyrrolic-N, and pyridinic-N-oxide. Each group’s bonding configuration, formation mechanism, and catalytic activity are analysed in detail to establish their distinct roles in modulating charge transfer, electron density distribution, and surface reactivity. Collectively, these functional moieties endow N-G with enhanced electrical conductivity, active sites for catalysis, and improved stability compared to pristine graphene. The chapter also underscores the critical correlations between synthesis conditions, defect types, and resultant functionalities, emphasizing their implications in applications such as oxygen reduction reactions (ORR), batteries, supercapacitors, and optoelectronic systems. Through this integrative examination, the chapter establishes a fundamental understanding of how atomic-level chemical modifications govern macroscopic performance, providing a knowledge base for the rational design of next-generation N-doped carbon nanomaterials with superior physicochemical and catalytic properties.