Our bodies are mostly bacteria. A new book reveals this crucial, invisible world

When Antony van Leeuwenhoek, the late 17th-century drape maker turned amateur scientist, first described microbes, people thought he was crazy. He focused his homemade microscopes on water from a pond outside his house, and on the dental plaque from his neighbors in Delft, the Netherlands. And he became the very first person to see a teeming world of life previously inaccessible to the human eye.

 Our Microbiomes Are Making Scientists Question What it Means to Be Human

Are we people or a "megaorganism?"

 We Are Our Bacteria

We may think of ourselves as just human, but we’re really a mass of microorganisms housed in a human shell. Every person alive is host to about 100 trillion bacterial cells. They outnumber human cells 10 to one and account for 99.9 percent of the unique genes in the body.

A Look at the Trillions of Microorganisms That Live in and on You

Scientists are continuing to learn what the microbiome does for our health, and how certain diseases and disorders are associated with changes in your microbes.

Engineering the Human Microbiome Shows Promise for Treating Disease

Synthetic biology may lead to the creation of smart microbes that can detect and treat disease.

Enter the Vaginome: Meet the Microbes that Live in Our Vaginas

We've gone way beyond Lactobacillus.

Germs Are Us

The process of learning about our microbiome is in its early days, but even the most tentative results have begun to transform our understanding of human health.

Me, myself, us

Looking at human beings as ecosystems that contain many collaborating and competing species could change the practice of medicine.

Meet the trillions of viruses that make up your virome

If you think you don’t have viruses, think again. It may be hard to fathom, but the human body is occupied by large collections of microorganisms, commonly referred to as our microbiome, that have evolved with us since the early days of man. Scientists have only recently begun to quantify the microbiome, and discovered it is inhabited by at least 38 trillion bacteria. More intriguing, perhaps, is that bacteria are not the most abundant microbes that live in and on our bodies. That award goes to viruses.

Some of My Best Friends Are Germs

Compared to a rain forest or a prairie, the interior ecosystem is not well understood, but the core principles of ecology — which along with powerful new sequencing machines have opened this invisible frontier to science — are beginning to yield some preliminary answers and a great many more intriguing hypotheses.

The 19th-Century Crank Who Tried to Tell Us About the Microbiome

The French chemist Antoine Béchamp (1816–1908) was a life-long rival to the great microbiologist Louis Pasteur. Pasteur invented pasteurization and vaccines for rabies and anthrax and discovered that many diseases are caused by invisible germs. Béchamp was a bitter crank who argued that microbes became dangerous when the health of the host—its “terrain” or environment—deteriorated.