The tumor microenvironment (TME) comprises both cellular components—including cancer cells and non-malignant immune and stromal cells—and non-cellular components, such as the extracellular matrix. Through intricate signaling interactions, these elements collectively regulate tumor initiation, progression, metastasis, and resistance to anticancer therapies. Consequently, targeting and modulating the TME offers novel and valuable insights into the complex mechanisms driving tumor heterogeneity and disease progression. Given recent advances in nanomedicine, a variety of sophisticated 3D scaffolds with favorable physicochemical properties have been developed to model the TME and serve as localized delivery platforms. In particular, TME-responsive scaffolds are noteworthy for their capacity to respond to key components and signals within the TME. Here, we review the classification, characteristics, and functional roles of the key components of the TME. This review also highlights the applications, advancements, and future prospects of 3D scaffolds, focusing on their use in 3D TME modeling and localized delivery systems. Furthermore, we discuss the limitations of conventional TME modeling and drug delivery systems and provide future perspectives on 3D scaffolds.