Welcome to the Nature Reviews Systems Biology collection — a
selection of recent Reviews, Perspectives and Research
Highlights, designed to provide an introduction to this emerging
cross-disciplinary field.

Once upon a time, scientists were satisfied with the characterization of
individual genes and proteins; a task that would frequently keep a single person, or several laboratories, occupied for years. The goal posts then shifted and the focus moved towards using genetics and biochemistry to dissect whole pathways. But our ambition has taken us beyond this focus — now the goal is to understand the intricate connections between individual pathways and entire networks.

Together, these connections govern the behaviours of cells, tissues and, ultimately,whole organisms. This ambitious aim is the focus of systems biology. Despite being ambitious, the goal is not unrealistic. The claim that we can understand systems in their entirety is bolstered by recent technological developments.Here, the focus has been on parallel analysis, high throughput, miniaturization and cost reduction. In their Review on page 9, Anne Carpenter and David Sabatini provide an overview of high-throughput systematic functional screens. Initiated in yeast, they can now be conducted in higher organisms, including human cells. Just as developments in robotics and technology revolutionized
biotechnology, concepts from physics, network theory in particular, have
had an important role in shaping our thinking about data that are
emerging from high-throughput experiments. On page 21, László Barabasi and Zoltán Oltvai explain how the principles of network theory can provide insights into systems biology and how it allows us to identify
universal laws that govern molecular networks.

Our understanding of basic biology provides important insights into
disease states, and systems biology is no exception. Knowledge of the
system’s components and its behaviour under normal conditions helps us to understand and might even allow us to predict how this behaviour
changes when these conditions are perturbed. An Opinion article by
Hiroaki Kitano and a Review by Jason Papin and colleagues explain how
principles of robustness and cellular networks can be used to study disease and result in the design of new therapies.

The print collection that you are holding is accompanied by a web focus
(http://www.nature.com/reviews/focus/systemsbiology). Here you will find additional Reviews, Perspectives and Research Highlights of recently
published, top primary papers in the field, as well as Research Articles from the Nature Publishing Group.Access to the Systems Biology web focus was provided free until October 2005. We are very grateful to Sigma-Aldrich for their financial support, which was instrumental in the production of this
collection.