Abstract: Tumor cells and the tumor microenvironment interact through molecular and cellular mechanisms to promote tumorigenesis and tumor migration. The tumor microenvironment is important in tumorigenesis and tumor progression. Tumor-associated macrophages (TAMs), which are ones of the most inflammatory cells in the tumor microenvironment, have significant influence on tumor development. Tumor cells recruit macrophages by releasing chemokines, cytokines, and growth factors, and switch them into M2-type macrophages. Macrophages also release many factors which are important to some stages of tumor development, including tumor growth, angiogenesis, migration, invasion, and distant metastasis. TAM density is associated with treatment failure and poor prognosis in tumor patients. Great progress has recently been made in targeting TAMs for anti-tumor therapy. Strategies of targeting TAMs for anti-tumor therapy include suppression of macrophage recruitment, inhibition of TAM viability, reinstating the TAM phenotype, and transforming M2-type macrophages to M1-type macrophages. This article reviews the latest progress in the field based on TAM functions.