Chemoselective ligation reactions provide facile access to various peptides and proteins including cyclic peptides, posttranslationally modified proteins, and peptide/ protein probes. Recently, peptide-ligase-based chemo-enzymatic methods have emerged as promising alternatives to chemical approaches. Ligation mediated by the newly discovered butelase 1 represents one of the state-of-the-art chemo-enzymatic strategies for its high catalytic efficiency and unique substrate specificity. The butelasemediated ligation can be carried out in a semisynthetic manner, in which chemically synthesized peptides and expressed proteins are used as substrates, rendering it suitable for various applications including site-specific modification of proteins and the preparation of thioesters. In this review, we summarize the recent studies and applications of butelase 1.