Fluid therapy involves replacing lost fluids and electrolytes to maintain homeostasis. Historically, saline solutions and Ringer's solution were developed and used to treat cholera victims and experimented on frog hearts. Common fluids include 0.9% saline, Ringer's lactate, 5% dextrose, Hartmann's solution, and Isolyte solutions. Indications for fluid selection depend on the fluid deficit and electrolyte abnormalities present. Special situations may require specific fluids like sodium bicarbonate or blood products.