Motivic integration is a notion in algebraic geometry that was introduced by Maxim Kontsevich in 1995 and was developed by Jan Denef and François Loeser.
 Since its introduction it has proved to be quite useful in various branches of algebraic geometry, most notably birational geometry and singularity theory.
 Roughly speaking, motivic integration assigns to subsets of the arc space of an algebraic geometry, a volume living in the Grothendieck ring of algebraic varieties.
 The naming 'motivic' mirrors the fact that unlike ordinary integration, for which the values are real numbers, in motivic integration the values are geometric in nature.
In the mathematical theory of knots, the Kontsevich invariant, also known as the Kontsevich integral of an oriented framed link, is a universal Vassiliev invariant in the sense that any coefficient of the Kontsevich invariant is of a finite type, and conversely any finite type invariant can be presented as a linear combination of such coefficients.
 It was defined by Maxim Kontsevich.
Gregori Aleksandrovich Margulis (Russian: Григо́рий Алекса́ндрович Маргу́лис , first name often given as Gregory, Grigori or Grigory; born February 24, 1946) is a Russian-American mathematician known for his work on lattices in Lie groups, and the introduction of methods from ergodic theory into diophantine approximation.
 He was awarded a Fields Medal in 1978 and a Wolf Prize in Mathematics in 2005, becoming the seventh mathematician to receive both prizes.
 In 1991, he joined the faculty of Yale University, where he is currently the Erastus L. De Forest Professor of Mathematics.
Operad theory is a field of abstract algebra concerned with prototypical algebras that model properties such as commutativity or anticommutativity as well as various amounts of associativity.
 Operads generalize the various associativity properties already observed in algebras and coalgebras such as Lie algebras or Poisson algebras by modeling computational trees within the algebra.
 Algebras are to operads as group representations are to groups. Originating from work in algebraic topology by Boardman and Vogt, and J. Peter May, it has more recently found many applications, drawing for example on work by Maxim Kontsevich and Thomas Willwacher on graph homology.
Letters in Mathematical Physics is a peer-reviewed scientific journal in mathematical physics published by Springer Science+Business Media.
 It publishes letters and longer research articles, occasionally also articles containing topical reviews.
 It is essentially a platform for the rapid dissemination of short contributions in the field of mathematical physics.
 In addition, the journal publishes contributions to modern mathematics in fields which have a potential physical application, and developments in theoretical physics which have potential mathematical impact.
 The editors are Volker Bach, Edward Frenkel, Maxim Kontsevich, Dirk Kreimer, Nikita Nekrasov, Massimo Porrati, and Daniel Sternheimer.
In mathematics, the Kontsevich quantization formula describes how to construct a generalized ★-product operator algebra from a given arbitrary Poisson manifold.
 This operator algebra amounts to the deformation quantization of the corresponding Poisson algebra.
 It is due to Maxim Kontsevich.
The napkin folding problem is a problem in geometry and the mathematics of paper folding that explores whether folding a square or a rectangular napkin can increase its perimeter.
 The problem is known under several names, including the Margulis napkin problem, suggesting it is due to Grigory Margulis, and the Arnold's rouble problem referring to Vladimir Arnold and the folding of a Russian ruble bank note.
 Some versions of the problem were solved by Robert J. Lang, Svetlana Krat, Alexey S. Tarasov, and Ivan Yaschenko.
 One form of the problem remains open.
In differential geometry, a subfield of mathematics, the Margulis lemma (named after Grigory Margulis) is a result about discrete subgroups of isometries of a non-positively curved Riemannian manifolds (e.g. the hyperbolic n-space).
 Roughly, it states that within a fixed radius, usually called the Margulis constant, the structure of the orbits of such a group cannot be too complicated.
 More precisely, within this radius around a point all points in its orbit are in fact in the orbit of a nilpotent subgroup (in fact a bounded finite number of such).
Maxim Lvovich Kontsevich (Russian: Макси́м Льво́вич Конце́вич ;   ; born 25 August 1964) is a Russian and French mathematician.
 He is a professor at the Institut des Hautes Études Scientifiques and a distinguished professor at the University of Miami.
 He received the Henri Poincaré Prize in 1997, the Fields Medal in 1998, the Crafoord Prize in 2008, the Shaw Prize and Fundamental Physics Prize in 2012, and the Breakthrough Prize in Mathematics in 2014.
In mathematics, specifically in symplectic topology and algebraic geometry, one can construct the moduli space of stable maps, satisfying specified conditions, from Riemann surfaces into a given symplectic manifold.
 This moduli space is the essence of the Gromov–Witten invariants, which find application in enumerative geometry and type IIA string theory.
 The idea of stable map was proposed by Maxim Kontsevich around 1992 and published in .

Question: What was the name of the medal that both Maxim Kontsevich & Grigory Margulis received?
Answer: Fields Medal