The study provides a comprehensive, single-cell and spatial transcriptomic analysis of the mouse female reproductive tract (FRT) during estrous cycling, pregnancy, and aging. Key findings include: 1. **Estrous Cycling and Immune Inflammation**: The FRT undergoes significant remodeling during the estrous cycle, with the vagina and cervix showing the most variable cell types and immune cell infiltration. Inflammation and extracellular matrix (ECM) remodeling are recurrent in these areas, driven by fibroblasts. 2. **Uterine Epithelial to Stromal Remodeling**: The uterus shows dramatic changes in epithelial to stromal ratio, with stromal proliferation peaking at the metestrus phase due to progesterone, while epithelial proliferation is highest at proestrus due to estrogen. 3. **Fibroblast Functions**: Fibroblasts play a central role in organizing ECM and regulating inflammation. Their functions are highly organ-specific, with different patterns of inflammatory and ECM-related gene expression in the upper and lower FRT. 4. **Spatial Analysis**: Spatial transcriptomics reveals that inflammatory fibroblasts shape the microenvironment of other fibroblasts, rather than immune cells. Fibroblasts are primary consumers of inflammatory and ECM cytokines. 5. **Decidualization**: Mouse decidual cells display an anti-inflammatory profile, similar to human decidual cells, and the transition to decidualization is largely conserved between mouse and human. 6. **Aging and Fibrosis**: Aging leads to primordial follicle depletion and immune cell infiltration in the upper FRT. Fibroblast inflammation and ECM remodeling accumulate with age, leading to fibrosis in the oviduct, uterus, and vagina. The intensity of ECM remodeling during the estrous cycle predicts the severity of age-related fibrosis. 7. **Cycling and Fibrosis**: Premature termination of cycling in young mice reduces fibrosis in the uterus and oviduct, suggesting that cycling contributes to fibrosis development through incomplete resolution of ECM remodeling. Overall, the study reveals how recurrent remodeling during the reproductive lifespan contributes to age-related fibrosis and chronic inflammation in the FRT.The study provides a comprehensive, single-cell and spatial transcriptomic analysis of the mouse female reproductive tract (FRT) during estrous cycling, pregnancy, and aging. Key findings include: 1. **Estrous Cycling and Immune Inflammation**: The FRT undergoes significant remodeling during the estrous cycle, with the vagina and cervix showing the most variable cell types and immune cell infiltration. Inflammation and extracellular matrix (ECM) remodeling are recurrent in these areas, driven by fibroblasts. 2. **Uterine Epithelial to Stromal Remodeling**: The uterus shows dramatic changes in epithelial to stromal ratio, with stromal proliferation peaking at the metestrus phase due to progesterone, while epithelial proliferation is highest at proestrus due to estrogen. 3. **Fibroblast Functions**: Fibroblasts play a central role in organizing ECM and regulating inflammation. Their functions are highly organ-specific, with different patterns of inflammatory and ECM-related gene expression in the upper and lower FRT. 4. **Spatial Analysis**: Spatial transcriptomics reveals that inflammatory fibroblasts shape the microenvironment of other fibroblasts, rather than immune cells. Fibroblasts are primary consumers of inflammatory and ECM cytokines. 5. **Decidualization**: Mouse decidual cells display an anti-inflammatory profile, similar to human decidual cells, and the transition to decidualization is largely conserved between mouse and human. 6. **Aging and Fibrosis**: Aging leads to primordial follicle depletion and immune cell infiltration in the upper FRT. Fibroblast inflammation and ECM remodeling accumulate with age, leading to fibrosis in the oviduct, uterus, and vagina. The intensity of ECM remodeling during the estrous cycle predicts the severity of age-related fibrosis. 7. **Cycling and Fibrosis**: Premature termination of cycling in young mice reduces fibrosis in the uterus and oviduct, suggesting that cycling contributes to fibrosis development through incomplete resolution of ECM remodeling. Overall, the study reveals how recurrent remodeling during the reproductive lifespan contributes to age-related fibrosis and chronic inflammation in the FRT.