Head and neck cancers (HNCs), predominantly squamous cell carcinomas, exhibit high relapse and poor survival rates despite multimodal treatment approaches. One of the main challenges in HNC is the tumor microenvironment (TME), which is composed of both immune and non-immune cells, as well as non-cellular components such as the extracellular matrix, which collectively foster an immunosuppressive environment that enables tumor growth, invasion, and therapeutic resistance. This chapter explores the intricate nature of the TME in HNC and its pivotal role in influencing treatment outcomes, particularly with immunotherapy. It delves into the characteristics and functions of key cellular components of the TME, including cancer-associated fibroblasts, dendritic cells, T cells, B cells, tumor-associated macrophages, and neutrophils, each presenting both challenges and therapeutic opportunities. Furthermore, it explores novel therapeutic strategies that target the TME, such as immune checkpoint inhibitors, adoptive cell transfer, and cancer vaccines. Additionally, it discusses predictive and prognostic factors related to immune, genetic, and microbial signatures in HNC, offering insights into their potential role in improving treatment outcomes. By exploring both current and emerging therapies, the present chapter underscores the significance of modulating the TME to enhance the efficacy of cancer treatments.