A pen is a writing tool used to apply ink to a surface such as paper for writing or drawing. Historically, reed pens, goose feather pens and water pens were used, with ink on the tip. Ruler pens can adjust the line width precisely, and some special uses can still be found, but technology pens such as rapidograph are more commonly used. Modern types also include ballpoint pens, roller hockey balls, fountains and felt or ceramic tipped pens.

Ballpoint pens distribute oil-based ink by rolling a small hard ball (usually 0.5-1.2 mm), made of brass, steel, or tungsten carbide. The ink dries almost immediately when it comes into contact with the paper. Ballpoint pens are usually reliable and are cheap and expensive. It has replaced pen as the most commonly used tool in daily writing.