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Osteosarcoma (OS), the most common primary malignant bone tumor in children and young adults, is characterized by aggressive behavior, frequent metastasis, and resistance to chemotherapy, resulting in poor clinical outcomes. Increasing evidence indicates that OS progression is not solely driven by tumor-intrinsic factors but is strongly influenced by dynamic interactions within the tumor microenvironment (TME). This literature review synthesizes current research on the roles of endothelial cells, fibroblasts, mesenchymal stromal cells, immune populations, and osteoclasts in OS pathogenesis, with emphasis on cell-cell interactions mediated by direct contact, soluble factors, and extracellular vesicles. The studies demonstrate that these interactions promote tumor proliferation, immune evasion, extracellular matrix remodeling, metastatic dissemination, and therapeutic resistance. Adaptive responses of both tumor and stromal cells to environmental stressors contribute to chemoresistance and disease progression. Collectively, our findings highlight the multifactorial nature of OS driven by complex cellular crosstalk within the TME. Understanding these mechanisms highlights the limitations of conventional chemotherapy and encourages the development of combined therapeutic approaches, including targeted therapies, immunomodulation, and microenvironmental interventions. Continued investigation into tumor-microenvironment interactions may facilitate the identification of actionable targets and improve personalized treatment approaches for OS.