There are times in the development of science when a shift in approach is sufficiently extensive that only a collection of thoughts and perspectives from many different practitioners can do justice to it. This issue sees the launch of a themed series of essays, called Connections, which take such an approach to the interdisciplinary study of complex, dynamic systems (see page 369).

Deeper insight requires a systems-level approach that seeks to understand interactions and make connections.

Scientists in almost every discipline are grappling with the problem of how best to model such systems. Cell biologists are being driven to do so, for example, by the surge of data from techniques that reveal biological processes in unprecedented detail, and quantum physicists by properties exhibited by collections of particles that would not have been anticipated on the basis of how a single particle behaves. Across these fields and beyond, deeper insight requires a systems-level approach that seeks to understand interactions and make connections. Although the goal is clear enough, the way to reach it is not.

Many researchers recoil from terms such as 'systems biology' and 'complexity,' interpreting them as euphemisms for things we don't adequately understand. Research on problems involving dynamic interactions between large numbers of entities is often directed by the availability of the data, rather than by a carefully considered question. And a rush of studies claiming to uncover simplifying principles that unite complex networks has sometimes generated more heat than light.

In some cases, attempts to understand networks and whole systems are driving researchers to cross disciplinary boundaries. Social and physical scientists are often more accustomed to such collective activity than molecular biologists, for whom the borrowing of techniques and expertise is now becoming commonplace.

The essays in the Connections series will illustrate some of the insights that are emerging as researchers pursue more holistic approaches to problems, while engaging in an unprecedented degree of collaboration between biological, social and physical scientists. They will raise provocative ideas about how to probe dynamic systems, illustrating, for example, how systems approaches can challenge assumptions established within the more reductionist framework of twentieth-century science.

The series begins just a few weeks after the popular Essay page returned to Nature. It will reiterate the tradition of this format as a forum for scientists to reflect on new ideas, or re-evaluate old ones. The Connections essays will also be collated on the web, where access to the first four will be free. We hope that, week by week, a greater story develops than could be told by a single article — and that over the coming year, the Essay page will continue to provide scientists with a valuable opportunity to say exactly what they think.

The Connections series of essays will be collected in this web focus.