Locked nucleic acid (LNA) is a nucleic acid analog containing one or more LNA nucleotide monomers with a bicyclic furanose unit locked in an RNA-mimicking sugar conformation. This conformational restriction is translated into unprecedented hybridization affinity towards complementary single-stranded RNA molecules. That makes fully modified LNAs, LNA/DNA mixmers, or LNA/RNA mixmers uniquely suited for mimicking RNA structures and for RNA targeting in vitro or in vivo. The focus of this chapter is on LNA antisense, LNA-modified DNAzymes (LNAzymes), LNA-modified small interfering (si)RNA (siLNA), LNA-enhanced expression profiling by real-time RT-PCR and detection and analysis of microRNAs by LNA-modified probes.