Endometrial cancer is one of the most common gynecological malignancies and is increasingly diagnosed in younger women, highlighting the growing need for fertility-preserving treatments. Progestin therapy using agents, such as medroxyprogesterone acetate and megestrol acetate, offers a non-surgical option for managing atypical endometrial hyperplasia and early-stage endometrial cancer in patients who desire to conceive. This chapter explores the efficacy and challenges of progestin therapy with complete response rates between 67% and 98.5%. Combination approaches, such as those incorporating levonorgestrel-releasing intrauterine devices or metformin, show promise for improving treatment outcomes. However, recurrence remains a significant concern, particularly in patients with endometrioid carcinoma grade 1. Genomic factors, including microsatellite instability-high/mismatch repair deficient status and Lynch syndrome, may further influence treatment success and risk of recurrence. Although progestin therapy provides a critical option for fertility preservation, careful patient selection, close monitoring for complications, such as thrombosis and liver dysfunction, and prompt transition to infertility treatment are essential. This chapter emphasizes the need for continued studies on the molecular subtypes and genetic predictors to refine treatment strategies and improve long-term outcomes in patients undergoing fertility-sparing treatment.