A fuel composition comprising a Fischer-Tropsch derived middle distillate fuel and a middle distillate flow improver, the remainder being another fuel component or mixture of fuel components. The other fuel component is selected from petroleum derived middle distillate fuel, hydrogenated vegetable oil, fatty acid methyl esters, and other Fischer Tropsch products. The Fischer-Tropsch derived middle distillate fuel is more than 80% v/v of the total composition; the maximum weight content in the carbon number distribution of the n-paraffins in the Fischer-Tropsch derived middle distillate fuel is below C16 and the weight ratio of iso to normal paraffins in the Fischer-Tropsch derived middle distillate fuel is 3.5:1 or higher. The middle distillate flow improver is a substituted ethylene polymer.