Nanomedicine that consists of using nanotechnology-based therapeutics has proven to be very useful in oncology, being widely exploited for the administration of chemotherapeutics as they allow the selective administration of these drugs at the tumor level, restricting their access to other areas of the organism and, consequently, diminishing their adverse effects. It has been widely demonstrated that the immune system plays a crucial role in the development and growth of carcinomas. The tumor immune microenvironment is characterized by the infiltration of immunosuppressive cells, such as M2-like macrophages, regulatory T lymphocytes, and myeloid-derived suppressor cells that create a tumor growth-supporting microenvironment, allowing tumor cells to progress and spread. In this context, the modulation and reprogramming of this immunosuppressive environment by targeting these immunosuppressive cells represent a potential anticancer approach as it allows the transformation of this tumor-supportive immune system to an antitumor immune response. Nanomedicine is an excellent tool to target all these tumor immunosuppressive cells. Targeting antigen-presenting cells is also a good strategy to promote an antitumor immune response. This chapter discusses the different nanoformulations targeting immunosuppressive tumor microenvironment and antigen-presenting cells that have been developed with the aim of boosting an antitumor immune response. Most formulations have been designed to target M2-like macrophages to convert them into M1-like macrophages that inhibit the growth of tumors, or to target dendritic cells to induce an antitumor immune response mediated by cytotoxic T-lymphocytes.