Permutahedra and Associahedra: Generalized associahedra from the   geometry of finite reflection groups
  This is a chapter in an upcoming Tamari Festscrift. Permutahedra are a class of convex polytopes arising naturally from the study of finite reflection groups, while generalized associahedra are a class of polytopes indexed by finite reflection groups. We present the intimate links those two classes of polytopes share. 
Christophe Hohlweg
math.CO math.GR