Introduction

    Chemistry is the science of the structure and transformation of non-living and living matter . It plays a basic role in the path towards understanding how matter has become complex, from the atom to the thinking organism in the course of the evolution of the universe .
    Molecular chemistry has developed a wide range of very powerful procedures for mastering the organisation of matter and building ever more complicated molecules from atoms linked by covalent bonds.
   Supramolecular chemistry lies beyond molecular chemistry . It aims at constructing and implementing highly complex chemical systems from molecular components held together by non-covalent intermolecular forces . It has relied on the development of preorganized molecular receptors for effecting molecular recognition, catalysis and transport processes, on the basis of the molecular information stored in the covalent framework of the components and read out at the supramolecular level through specific interactional algorithms. By combination of suitable molecular components, it has explored the design of functional supramolecular devices presenting photonic, electronic, ionic and mechanic properties. 
     A further step consists in the design of systems undergoing self-organization, i.e. systems capable of spontaneously generating well-defined functional supramolecular architectures by self-assembly from their components, thus behaving as programmed chemical systems. Chemistry may therefore also be considered as an information science, the science of informed matter .
     The design of molecular information controlled, “programmed” and functional self-organizing systems provides an original approach to nanoscience and nanotechnology. It represents a means of performing programmed engineering and processing of functional nanostructures. It offers a very powerful complement or alternative to nanofabrication .
     Supramolecular chemistry is intrinsically a dynamic chemistry in view of the lability of the interactions connecting the molecular components of a supramolecular entity and the resulting ability of supramolecular species to exchange their constituents. The same holds for molecular chemistry when the molecular entity contains covalent bonds that may form and break reversibility, so as to allow a continuous change in constitution by reorganization and exchange of building blocks. These features define a Constitutional Dynamic Chemistry (CDC) on both the molecular and supramolecular levels.
      CDC introduces a paradigm shift with respect to constitutionally static chemistry. It takes advantage of dynamic diversity to allow variation and selection. The implementation of selection in chemistry introduces a fundamental change in outlook. Whereas self-organization by design strives to achieve full control over the output molecular or supramolecular entity by explicit programming, self-organization with selection operates on dynamic constitutional diversity in response to either internal or external factors to achieve adaptation.
    In the process of reaching higher levels of self-organisation, CDC gives access to the generation of networks of dynamically interconverting constituents connected either structurally (molecular and supramolecular arrays) or reactionnally (set of connected reactions) or both. They define a class of constitutional dynamic networks (CDNs), presenting agonistic and antagonistic relationships between their constituents, that may couple to thermodynamic or kinetic processes and respond to perturbations by physical stimuli or to chemical effectors.

   The merging of the features: - information and programmability, - dynamics and structural diversity, constitution and connectivity opens vast perspectives and points towards the emergence of adaptive and evolutive chemistry, towards systems of increasing complexity and a science of complex matter.