PHD, with variations in capitalization and punctuation, is a three letter acronym that may refer to:

  • Ph.D., the academic degree of Doctor of Philosophy
  • Ph.D. (band), a 1980s British group
  • PHD finger, a protein sequence
  • PHD Mountain Software, an outdoor clothing and equipment company
  • PhD Docbook renderer, an XML renderer
  • PhD: Phantasy Degree, a Korean comic series
  • PHD, an Italian pizza shop based in Hong Kong
  • Phospholipid
  • Piled Higher and Deeper, a web comic
  • Parisada Hindu Dharma, an Indonesian reform organization
  • Pisarenko harmonic decomposition, a method of frequency estimation
  • Prolyl hydroxylase, an enzyme
  • "PHD", a song by the Crystal Method from Tweekend
  • Post hole digger