The recent discovery that the human and other mammalian genomes produce thousands of long non-coding RNAs (lncRNAs) raises many fascinating questions. These mRNA-like molecules, which lack significant protein-coding capacity, have been implicated in a wide range of biological functions through diverse and as yet poorly understood molecular mechanisms. Despite some recent insights into how lncRNAs function in such diverse cellular processes as regulation of gene expression and assembly of cellular structures, by and large, the key questions regarding lncRNA mechanisms remain to be answered. In this review, we discuss recent advances in understanding the biology of lncRNAs and propose avenues of investigation that may lead to fundamental new insights into their functions and mechanisms of action. Finally, as numerous lncRNAs are dysregulated in human diseases and disorders, we also discuss potential roles for these molecules in human health.