In the past decade marine microbiology has emerged as an important and dynamic discipline. To mark the significant progress enjoyed by this exciting field, Nature Reviews Microbiologyhas specially commissioned a collection of articles that highlight the latest advances and how they are leading to a new understanding of biodiversity, ecology and biogeochemistry.

Vaccines are among the most useful and cost-effective tools for reducing the morbidity and mortality associated with infectious diseases. This special Focus issue highlights some of the latest progress in vaccine development and the pitfalls that have been encountered along the way.

In recent years, it has become increasingly evident that HGT is central to microbial activities that influence both our health and the environment - it is also clear that the exploitation of HGT holds great promise as an instrument for their improvement.

Metagenomics is based on the genomic analysis of microbial DNA that is extracted directly from communities in environmental samples.Metagenomics could also unlock the massive uncultured microbial diversity present in the environment to provide new molecules for therapeutic and biotechnological applications.

In 2004, infectious diseases are still the second leading cause of death worldwide, the number of emerging or re-emerging bacterial, fungal and viral pathogens continues to increase, and the threat of bioterrorism looms large worldwide.Thus, the need for new antimicrobial agents is perhaps greater now than it has ever been, and with the lack of new anti-infectives in the pipeline, there is great interest in innovative strategies.

Innate immunity is the first line of defence against pathogens and is initiated rapidly after recognition of microbial products by receptors such as the Toll-like receptors (TLRs). We outline the signalling cascades initiated by TLR triggering and the therapeutic potential of targeting this pathway, as well as relevant Highlight articles from the journal.

This collection, along with other analysis of key components of the ocean's food web, highlights the significance of genome sequences from the sea. We powerfully demonstrate how genomics can lead to a new understanding of biodiversity, ecology and biogeochemistry.

In March 2003, the World Health Organization issued global warnings about a mysterious and deadly form of pneumonia. Our reporters pose key questions about the outbreak, and assess our preparedness to deal with future viral threats.

This focus provides a broad picture of the importance of microbial genetics but, more than this, they show that the answers to the big questions that were provided by this field in the past might be the tip of an iceberg that looms large in the future.

The term 'weapons of mass destruction' seems destined to be one of those rare pieces of jargon that insinuates itself into common usage. The reason for this dubious honour is, of course, that the deployment of such weapons, particularly agents of bioterror, has rarely seemed as possible as it does today. For the same reason, the question of biodefence - defence against agents of bioterror - is high on the agendas of governments, the public and the research community.

Each year an estimated 8 million people develop clinical disease and 1.87 million people die of TB. These staggering numbers make tuberculosis one of the leading infectious disease killers. Although complete eradication of TB once seemed possible, the increasing incidence of multidrug resistant (MDR) strains, and the deathly specter of AIDS which increases the risk of developing TB 30-fold, means that we are now faced with reemergence of the disease as a global health emergency

Around 400 million people now suffer from the disease, with 130 million new cases occurring annually. The genome of the Anophelesmosquito has been mapped and is now being sequenced, and the complete genome sequence ofP.falciparumshould be at hand within the next year.