  This manuscript aims to provide a self-contained introduction to the
regularity theory for elliptic PDE, focusing on the main ideas rather than
proving all results in their greatest generality. It can be seen as a bridge
between an elementary PDE course and more advanced textbooks.
  This is a draft of the book "Regularity Theory for Elliptic PDE". The final
version has been published in Zurich Lectures in Advanced Mathematics, EMS
Press, 2022.
