Complex interactions among structural, endocrine, and molecular factors determine mare reproductive potential. This narrative review summarizes current research data on clinical, hormonal, and molecular–biochemical biomarkers associated with mare fertility and evaluates their potential use in reproductive assessment. Clinical assessment remains the foundation of reproductive evaluation and includes age, reproductive history, ultrasonography, cytology, bacteriology, and endometrial biopsy. Hormonal biomarkers such as anti-Müllerian hormone, estradiol, progesterone, and gonadotropins provide additional information on ovarian reserve, follicular activity, ovulation, and luteal competence. Increasing attention has also focused on molecular and biochemical biomarkers related to inflammation, oxidative stress, extracellular matrix remodeling, and embryonic–maternal communication. Despite growing interest in advanced biomarker approaches, many molecular indicators are not yet sufficiently validated for routine clinical use in mares. Small sample sizes, methodological heterogeneity, and a lack of standardized reference ranges often limit available studies. Therefore, interpretation of reproductive biomarkers should remain cautious and clinically contextualized. Available data suggest that integrating structural, endocrine, and molecular information may improve reproductive evaluation and enable more individualized management strategies in mares. However, prospective studies evaluating the predictive value and clinical utility of integrated biomarker models remain limited.