Macrophages are critical regulators of tissue homeostasis but are also abundant in the tumor microenvironment (TME). In both primary tumors and metastases, such tumorassociated macrophages (TAMs) seem to support tumor development. While we know that TAMs are the dominant immune cell in the TME, their vast heterogeneity and associated functions is only just being unraveled. In this review, we outline the various known TAM populations found thus far, and delineate their specialized roles associated with the main stages of cancer progression. We discuss how macrophages may prime the pre-metastatic niche to enable the growth of a metastasis and then how subsequent metastasis-associated macrophages can support secondary tumor grown. Finally, we speculate on the challenges that remain to be overcome in TAM research.