Three billion years ago, more or less, life crossed a threshold and began moving toward a multicellular existence. Evidence from multiple directions is showing how this hard-to-fathom leap might have been less difficult than once believed. The evolutionary histories of some groups of organisms record numerous transitions from single-celled to multicellular forms, suggesting the hurdles could not have been so high. Genetic comparisons between simple multicellular organisms and their single-celled relatives have revealed that much of the molecular equipment needed for cells to band together and coordinate their activities may have been in place well before multicellularity evolved. And clever experiments have shown that in the test tube, single-celled life can evolve the beginnings of multicellularity in just a few hundred generations—an evolutionary instant. The end result: the incredible diversity of life seen today.