Long noncoding RNAs (lncRNAs) are transcripts that are greater than 200nt, but do not encode a protein. Recent evidence shows that lncRNAs outnumber protein-coding genes. However, only a handful of lncRNAs have a defined function. Here we present some examples of functions of lncRNAs and a graph-theoretic framework for describing lncRNA structures. These methods will then be used to help classify lncRNAs by structure on a genome-wide scale. Furthermore, we present some examples of disease associated structural features of lncRNAs that could shed light on their function.