A roller ball pen is a writing instrument that came into being during the eighties. It combined the warm feeling of liquid ink (like a fountain pen) with the convenience of a ball point pen. Like the latter, the barrel contains a refill tipped with a rotating ball. As one moves the pen along the paper, the ink is transferred to it.

As they use a liquid ink, roller balls initially required a cap, rather than the retracting mechanism employed by most ball point pens, to prevent evaporation. More recently, retractable models have become common. Also, a gel ink has become popular. This ink has proven to be the most resistant to check washing (liquid ink (including the one used by fountain pens) is almost as good).

Roller ball pens generally are more expensive than ball point pens, but cheaper than fountain pens. There are also some very nice models.