Works about and related to Koestler

Introduction

Biographies
  Iain Hamilton: Koestler - A biography
  George Mikes: Arthur Koestler - the Story of a Friendship
David Cesarani: Arthur Koestler - The Homeless mind.
   

Essays and studies
  Jospeh Nedava: Arthur Koestler
John Atkins: Arthur Koestler
   
Other references
  Reed Merril & Thomas Frazier: Arthur Koestler - An international bibliography
   
Crossroads
  Alex Weissberg: Conspiracy of Silence