Na-ion batteries (SIBs) are increasingly recognized as sustainable alternatives to lithium-ion systems because sodium is abundant, low-cost, and environmentally compatible. However, developing high-performance anode materials remains a critical challenge. Among various candidates, heteroatom-doped hard carbons have attracted significant attention for their superior electrochemical performance, enhanced capacity retention, and structural stability. This review highlights recent advances in synthesizing and modifying heteroatom-doped hard carbons, focusing on strategies to incorporate nitrogen, sulfur, phosphorus, boron, and fluorine into carbon frameworks. This review critically examines how these dopants modulate electronic structure, introduce defects, and create more active sites, emphasizing their ability to enhance sodium-ion adsorption, diffusion, and overall kinetics. Fundamental sodium storage mechanisms such as adsorption, intercalation, and pore filling are discussed in relation to doping-induced changes, along with impacts on ion transport and charge-transfer resistance. By integrating insights from synthesis methodologies, structural engineering, and electrochemical behavior, this work provides a comprehensive understanding of the multifaceted role of heteroatom doping. The review aims to guide the rational design of heteroatom-doped hard carbon anodes, enabling next-generation Na-ion batteries with higher energy density, improved cycling stability, and greater commercial viability.