  This is a survey of recent results about bipotentials representing
multivalued operators. The notion of bipotential is based on an extension of
Fenchel's inequality, with several interesting applications related to non
associated constitutive laws in non smooth mechanics, such as Coulomb
frictional contact or non-associated Drucker-Prager model in plasticity.
  Relations betweeen bipotentials and Fitzpatrick functions are described.
Selfdual lagrangians, introduced and studied by Ghoussoub, can be seen as
bipotentials representing maximal monotone operators. We show that bipotentials
can represent some monotone but not maximal operators, as well as non monotone
operators.
  Further we describe results concerning the construction of a bipotential
which represents a given non monotone operator, by using convex lagrangian
covers or bipotential convex covers.
