Recently, several lines of evidence have suggested that noncoding RNAs, which include both small and long noncoding RNAs (ncRNAs), contribute to a significant portion of the transcriptome in eukaryotic organisms. However, the functional significance of this wide-spread occurrence of ncRNAs, and in particular, the long ncRNAs (lncRNAs), for organismal development and differentiation is unclear. The available evidence from a subset of lncRNAs suggests that certain lncRNAs, and/or the act of their transcription, are involved in important biological functions at the transcriptional and posttranscriptional level. This chapter discusses the epigenetic and nonepigenetic mechanisms by which lncRNAs and/or their transcription are involved in the programming of various biological functions in model systems, from yeast to mammals.