Macrophages not only are prominent effector cells of the immune system that are critical in inflammation and innate immune responses but also fulfill important functions in tissue homeostasis. Transcription factors can define macrophage identity and control their numbers and functions through the induction and maintenance of specific transcriptional programs. Here, we review the mechanisms employed by lineage-specific transcription factors to shape macrophage identity during the development from hematopoietic stem and progenitor cells. We also present current insight into how specific transcription factors control macrophage numbers, by regulating coordinated proliferation and differentiation of myeloid progenitor cells and self-renewal of mature macrophages. We finally discuss how functional specialization of mature macrophages in response to environmental stimuli can be induced through synergistic activity of lineage- and stimulus-specific transcription factors that plug into preexisting transcriptional programs. Understanding the mechanisms that define macrophage identity, numbers, and functions will provide important insights into the differential properties of macrophage populations under various physiological and pathological conditions.