1. Pathophysiology and Associations.- 2. Non-invasive diagnostics for Detrusor underactivity/Underactive bladder .- 3. Invasive Diagnostic Tests .- 4. Epidemiology of Underactive Bladder.- 5. Indications For Treatment .- 6. Pharmacologic Treatment of Underactive Bladder.- 7. Surgical Treatment : Outlet Reduction , Men and Women.- 8. Neurostimulation and Neuromodulation for the Treatment for the Underactive Bladder .- 9. Reduction Cystoplasty.- 10. Bladder Wrap Procedures.- 11. Tissue Engineering and cell therapy for underactive current and future approaches.- 12. Reflections and the Way Forward.