Nephrolithiasis is the medical term for kidney stones, hard mineral deposits that form in the renal pelvis or calyces when urine becomes supersaturated with stone-forming salts. Most stones are calcium oxalate, with smaller proportions of calcium phosphate, uric acid, struvite, and cystine. Diet plays a central role in both cause and prevention: low fluid intake concentrates urine, high sodium intake raises urinary calcium, excess animal protein acidifies urine, and high oxalate foods such as spinach and rhubarb can contribute in susceptible people. Countermeasures with good evidence include generous water intake, adequate dietary calcium to bind oxalate in the gut, and citrate from citrus fruit, which inhibits crystallisation. Recurrence is common, so dietary management usually continues long after the first stone passes.