The goal of this major undertaking is to support and enhance the interactions between mathematics and physics by making full use of the modern information technologies. Indeed, the 20^th century was full of dramatic discoveries in each domain. And the important advances of that century in mathematical physics demonstrate clearly that physics is much closer to deep problems in mathematics than one could imagine by studying textbooks in our universities, and that physical ideas and concepts are often seminal in mathematics.

The Modern Encyclopedia of Mathematical Physics (MEMPhys) is a truly 21^st century scientific encyclopedia, emphasizing mathematical physics as opposed to mathematics on one side and physics on the other. The central idea is to create a modern version of Maimonides’ Guide for the Perplexed, albeit limited to this multidisciplinary field. Indeed nowadays, increasingly so, the problem (especially in science) is not so much the existence or availability of information, but the ability to find, when the need occurs, pertinent and reliable information. So MEMPhys seeks to be a model for locating authoritative overviews and an efficient starting point for researchers and students at any level.

Moreover, mathematical physics is not just an intersection of mathematics with physics, and certainly not a disjoint union of topics in both, but the discipline has an intrinsic value and existence that is articulated throughout this work. Accordingly, the contributions are written in precise mathematical language with clear indication of heuristic aspects, with physical interpretations or applications serving as examples. The ability to interrelate distinct items in MEMPhys (such as connecting an entry from the Encyclopedia with material from a handbook as well as with many texts existing in electronic form) enhance that characteristic of MEMPhys. Since this reference anticipates and seeks as wide a scientific audience as possible, students of mathematical physics, physics, and mathematics readily find concise summaries of recent profound ideas and to get an stimulating idea of their interrelations.