For more than two decades we have known of the existence of a population of very dusty, far-infrared luminous sources at high redshift. But until the commissioning of ALMA, many of the basic characteristics of these sources were unclear. I will discuss recent studies with ALMA which are beginning to penetrate the obscuration in these systems to allow us to understand their fundamental properties. I will also discuss their connection to the formation and evolution of the galaxy populations we see in the Universe today.