Chagas disease is one of the most neglected of the tropical diseases, yet millions of people are infected with it. There are only two available drugs to treat it, both of which are more than 40 years old and neither of which is ideal. As the global population has become more internationally mobile, Chagas disease has spread from Latin America to become a worldwide threat. This Outlook highlights some of the progress in understanding and treating Chagas disease over its 101 years of recent history and outlines the challenges still to be met.

Natureinvestigates the metrics that shape scientific careers, from the citation index to the h-index and more.

Plasticity is the capacity of cells or organisms to vary their properties or behaviour when environmental conditions change. Studies over the past few decades have shown that cells are considerably more plastic than had been thought. Uncovering the molecular and cellular mechanisms underlying this plasticity is a dynamic area of biology and biomedicine.

Helper T cell heterogeneity was discovered two decades ago, initially with the designation of Th1 and Th2 cells, which are involved in immunity against intracellular and extracellular pathogens, respectively. Several years ago a third lineage was identified as the Th17 cells and several novel T cell subsets have since been found, including Treg and Tfh cells. The collection of articles presented in the May special issue and accompanying web focus summarize our understanding of the development and function of the T cell subsets in immunity and immune diseases.

On 24 04 1990, the Hubble Space Telescope was launched into a low Earth orbit. Now, 20 years on, Hubble continues to produce stunning images of the Solar System and the farthest reaches of the Universe. In this special, Naturepresents a retrospective, a slideshow and some archive stories about the iconic telescope. Happy Birthday Hubble!

Worldwide, the number of old people is increasing rapidly, so finding ways to keep age-related diseases at bay is an urgent task. Owing to a growing understanding of the processes that underlie ageing, there is hope that, at some time in the future, elderly people will be kept healthy by suppressing the ageing process itself.

Cancer research is progressing at a rapid pace. This Collection highlights recent studies that increase our understanding of the complex biological processes underlying tumour development and progression. They also feature novel approaches towards translating these advances into potential new anti-cancer drugs.

Natureexamines the gap between academia and the forensic lab, and explores ways in which the two areas can come together to put science in court on a stronger footing.

Bring together a large number of particles and they can order themselves in unusual ways. This can give rise to emergent phenomena that cannot be understood solely in terms of the interactions that rule at the microscopic level — a theoretical and experimental playground for physicists in which the maxim 'more is different' holds true in particularly striking ways.

Nature is delighted to present this biodiversity supplement for 2010, International Year of Biodiversity. As nations come together to reduce the alarming loss of species taking place worldwide, we hope that these features, opinion pieces, News & Views articles and original research papers will provide a useful snapshot of the problems faced and solutions proposed.

A cell is a self-organizing and self-replicating machine. The genome contains the instructions for building this highly complex machine, but how this information is accessed, read and interpreted depends on the cell type and its stage of development. Our understanding of how cellular organization and function are regulated in this way is now rapidly improving.

Why do we behave in the way that we do? This series of Essays reveals how the latest research is altering our understanding of what it is to be human. Whether in relation to religion or to our collective behaviour in cities, experts explore the potential impact on society, now and in the future, of discoveries in psychology, anthropology, genetics, neuroscience, game theory and network engineering.