**Abstract**

As a regulatory molecule of post-transcriptional gene expression, microRNA (miRNA) is a class of endogenous, non-coding small molecule RNAs. MiRNA detection is essential for biochemical research and clinical diagnostics but challenging due to its low abundance, small size, and sequence similarities. In this chapter, traditional methods of detecting miRNA like polymerase chain reaction (PCR), DNA microarray, and northern blotting are introduced briefly. These approaches are usually used to detect miRNA *in vitro*. Some novel strategies for sensing miR-NAs *in vivo*, including hybridization probe assays, strand-displacement reaction (SDR), entropy-driven DNA catalysis (EDC), catalytic hairpin assembly (CHA), hybridization chain reaction (HCR), DNAzyme-mediated assays, and CRISPRmediated assays are elaborated in detail. This chapter describes the principles and designs of these detection technologies and discusses their advantages as well as their shortcomings, providing guidelines for the further development of more sensitive and selective miRNA sensing strategies *in vivo*.

**Keywords:** microRNA, hybridization probe assays, strand-displacement reaction (SDR), entropy-driven DNA catalysis (EDC), catalytic hairpin assembly (CHA), hybridization chain reaction (HCR), CRISPR
