Introduced by the late Per Bak and his colleagues, self-organized criticality (SOC) has been one of the most stimulating concepts to come out of statistical mechanics and condensed matter theory in the last few decades, and has played a significant role in the development of complexity science. SOC, and more generally fractals and power laws, have attracted much comment, ranging from the very positive to the polemical. The other papers (Aschwanden et al., 2014; McAteer et al., 2014; Sharma et al., 2015) in this special issue showcase the considerable body of observations in solar, magnetospheric and fusion plasma inspired by the SOC idea, and expose the fertile role the new paradigm has played in approaches to modeling and understanding multiscale plasma instabilities.

Why is it that a whole can acquire properties that are not intrinsic to any of its parts? Many of us have been confronted with a situation where each member of a collective is «against» or hesitates, whereas the overall vote is affirmative. The same problem can be noticed in chemical kinetics. Chemical transformations take place at the molecular level, but oscillatory reactions exist where almost all of the molecules start to run synchronously, as if on a mutual agreement, or obeying the rule of an invisible director. In this case, the solution in the test tube can periodically change its color, becoming now blue, and now red. One of the fundamental problems in biology is that of morphogenesis. As believed by biologists, each cell has one and the same set of genes. Then how is it that these cells, in the course of the development of the organism, «know» which of them are to become brain cells, or which of them are to become heart cells? In 1952, the attempt of Alan Turing, one of the fathers of cybernetics, to construct an exceedingly simple model for explaining this selection, marked the birth of synergetics.

We review an emerging body of work by physicists addressing questions of economic organization and function. We suggest that, beyond simply employing models familiar from physics to economic observables, remarkable regularities in economic data may suggest parts of social order that can usefully be incorporated into, and in turn can broaden, the conceptual structure of physics. In the last decade or so physicists have begun to do academic research in economics in a newly emerging field often called “econophysics”. Perhaps a hundred people are now actively involved, with two new journals1 and frequent conferences. At least ten books have been written on econophysics in general or specific subtopics (We are restricted by citation limits here, but an extensive bibliography of the books and archived articles is maintained on the econophysics website, http://www.unifr.ch/econophysics).