Over the past two decades, synthetic bone substitutes—particularly in their injectable and resorbable forms—have emerged as crucial therapeutic tools for the reconstruction of complex bone defects in orthopedic surgery. These advanced biomaterials are specifically designed to mitigate the clinical reliance on traditional autografts, which often present complications such as donor site morbidity and limited supply. By offering the ability to precisely fill irregular anatomical cavities, these injectable materials create a highly effective osteoconductive scaffold that provides an optimal microenvironment for natural bone regeneration. The most prominent and clinically relevant families within this diverse group of biomaterials include calcium phosphates, calcium sulfate, hydroxyapatite (HA), beta-tricalcium phosphate (β-TCP), bioactive glasses, and advanced polymer-ceramic composites. The primary clinical advantages of these synthetic grafts lie in their seamless injectability, excellent biocompatibility, gradual resorption, and their unique capacity to conform perfectly to the complex geometry of a given bone defect. Despite these significant benefits, critical limitations continue to persist in clinical applications; these include inherent structural brittleness, challenges in controlling the rate of material resorption, pronounced mechanical weakness under high load-bearing conditions, and notable discrepancies between highly successful laboratory results and actual clinical outcomes. Through a comprehensive analytical and review-oriented approach, this article systematically examines the foundational biomaterial science, specific design requirements, current orthopedic applications, and the promising future trajectory of injectable synthetic bone grafts.