Gastric cancer (GC) is diagnosed more than one million times each year and represents a major cause of cancer-related death worldwide. Although GC presents as a group of different types of disease, chronic inflammation has been strongly associated with tumorigenesis. Monocyte/macrophage play important roles in the development of inflammation and are vital components of the tumor microenvironment (TME). Monocyte/macrophage exert protumor and/or antitumor effects through the release of angiogenic and lymphangiogenic factors. Furthermore, tumor associated macrophages (TAMs) are emerging as key players in GC development. It is necessary to review and elucidate the roles of TAM subsets in GC and their molecular features. In this study, we focused on GC-related subsets of monocytes/macrophages and analyzed signaling related to TAMs in GC as well as the potential roles of these cells as therapeutic targets.