笔是用于书写或绘画用的工具，多通过笔尖将带有颜色的固体或液体（墨水）在纸上或其他固体表面书写或绘画，也有利用固体笔尖的硬度比书写表面大的特性在表面刻出符号或图画。

现今普遍使用的是签字笔和圆珠笔，绘制艺术底稿和画图则多用铅笔。而古代，在中国，使用的是毛笔。古希腊、古罗马曾在木板面上涂蜡，然后用铁棒在蜡面上划写。古代埃及和波斯，曾将芦苇杆削尖当笔使用。从中世纪开始，在欧美，则是使用芦苇笔或鹅毛笔，两种笔因笔尖材质截然不同，毛笔为软质笔尖，写时圆转，粗细差别很大，而芦苇笔为硬质笔尖，写时方正多角。

今日笔的种类相当多种，生产方式也相当多样化。

A pen (Latin: penna, feather) is a writing implement used to apply ink to a surface, such as paper, for writing or drawing. Historically, reed pens, quill pens, and dip pens were used, with a nib dipped in ink. Ruling pens allow precise adjustment of line width, and still find a few specialized uses, but technical pens such as the Rapidograph are more commonly used. Modern types also include ballpoint, rollerball, fountain, and felt or ceramic tip pens.