Erectile dysfunction (ED) is the persistent inability to achieve or maintain an erection sufficient for satisfactory sexual performance, affecting approximately 50% of men aged 40-70 to some degree. Normal erection requires intact neurological pathways (parasympathetic nerves S2-S4 releasing nitric oxide), vascular integrity (arterial inflow through cavernosal arteries), smooth muscle relaxation (nitric oxide → cGMP → smooth muscle relaxation), and venous occlusion (compression of subtunical venules). ED is primarily vascular (70-80% of cases) due to endothelial dysfunction and atherosclerosis affecting penile arteries - the same process causing coronary artery disease. ED often precedes cardiovascular events by 2-5 years, serving as an early warning sign. Neurogenic causes include diabetic neuropathy, spinal cord injury, multiple sclerosis, and post-radical prostatectomy nerve damage. Psychogenic causes include performance anxiety, depression, and relationship issues. Medications (antihypertensives, SSRIs, antiandrogens) and endocrine disorders (hypogonadism, hyperprolactinemia) are other common causes.