The possibility of prehistoric Polynesian contact with the Americas has been considered by historians, archaeologists, and other scholars for centuries. Most evidence and most scholarly discourse have focused on South America, but as early as the 1930s, Alfred Kroeber suggested that cultural similarities between southern California and Oceania could be the product of prehistoric trans-oceanic diffusion. Here I review archaeological, linguistic, and other evidence for such contact in North and South America with an emphasis on recent genetic studies that challenge some longstanding ideas.