Long non-coding RNAs (lncRNAs) have gained widespread interest in the past decade owing to their enormous amount and surprising functions implicated in a variety of biological pro-cesses. Some lncRNAs exert function as enhancers, i.e., activating gene transcription by serving as the cis-regulatory molecules. Furthermore, recent studies have demonstrated that many enhancer elements can be transcribed and produce RNA molecules, which are termed as enhancer RNAs (eRNAs). The eRNAs are not merely the by-product of the enhancer transcription. In fact, many of them directly exert or regulate enhancer activity in gene activation through diverse mechanisms. Here, we provide an overview of enhancer activity, transcription of enhancer itself, characteristics of eRNAs, as well as their roles in regulating enhancer activity and gene expression.