PEN may refer to:

• PEN International, the worldwide association of writers
  • English PEN, the founding centre of PEN International
  • PEN American Center, the Eastern US branch in New York City
  • PEN Center USA, the Western US branch in Los Angeles
  • PEN Canada
• Penang International Airport in Penang, Malaysia (IATA airport code)
• Penarth railway station, Wales; National Rail station code PEN
• Peruvian nuevo sol, ISO 4217 currency code for the currency of Peru
• Polyethylene naphthalate, a polymer
• Private enterprise number, an object identifier in computing
• Protective earth neutral, an earthing system conductor in electricity supply systems
• Olympus Pen is a series of half-frame cameras made by Olympus from 1959 to the beginning of the 1980s
• PEN/Faulkner Foundation

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.