1. Introduction 2. FDA Approved Fused Pyrimidine-Based Drugs 3. Naturally occurring fused pyrimidine derivatives and Medicinal Attributes 4. Five-Membered Ring Fused Pyrimidine-Based Derivatives and Biological Properties 5. FDA approved Five-Membered Ring Fused Pyrimidine-Based Derivatives and Biological Properties 6. Benzene Fused Pyrimidine-Based Derivatives and their Biological Properties 7. Six-Membered Ring (with N, O or S) Fused Pyrimidine-Based Derivatives and Biological Properties 8. FDA approved Six-Membered Ring Fused Pyrimidine-Based Derivatives 9. Seven-Membered Ring Fused Pyrimidine-Based Derivatives and Biological Properties 10. Eight-Membered Fused Pyrimidine Derivatives and Biological Properties 11. Molecular Modeling Studies of Fused Pyrimidine Derivatives at various receptors