This mouse strain is constructed by placing the optimized iCre recombinase gene under the control of the colony-stimulating factor 1 receptor (Csf1r) gene promoter/enhancer, either as a transgene or via gene knock-in. Csf1r is a lineage marker gene for macrophages, monocytes, and their precursors, and is expressed in nearly all tissue macrophages (including brain microglia, liver Kupffer cells, alveolar macrophages, etc.) as well as circulating monocytes. This model drives efficient and specific expression of iCre recombinase in these Csf1r-positive cells. When crossed with reporter mice carrying LoxP sites (e.g., Rosa26-LSL-tdTomato) or conditionally modified mice (Floxed mice), it enables stable reporter gene expression or conditional gene knockout/activation throughout the myeloid cell lineage, particularly the macrophage lineage. This model is one of the most important and commonly used genetic tools for studying macrophage development, function, and their roles in tissue homeostasis, inflammation, cancer, and metabolic diseases.