Lettuce should look bright and bouncy: no browning or slimy patches.
Lettuces are traditionally stored stem end up, so that the milk flows down into the leaves.
Lettuces fall into four groups: butterhead (such as the ordinary round lettuce), crisphead (Iceberg or Webb's Wonder), loose leaf (such as Lollo Rosso) and Cos.
Romaine is the American and French name for Cos. Little Gem is a small variety.
Always dry salad lettuce thoroughly after washing, or the dressing won't cling to the leaves properly.
Lettuce makes us think of salad first, just as salad makes us think of lettuce. But don't dismiss recipes for cooked lettuce. You might think you would be left with nothing but a soggy mess, but in fact the results are surprisingly robust and make good eating.