Carbon-carbon bond formation is one of the most important topics in organic synthesis. One of the most powerful methods for constructing a carbon-carbon bond is the reductive coupling of carbonyl compounds giving 1,2-diols. Of these methods, the pinacol coupling, which was described in 1859, is still a useful tool for the synthesis of vicinal diols. 1, 2-Diols obtained in the reaction were very useful synthons for a variety of organic synthesis, and were also used as intermediates for the construction of biologically important natural product skeletons and asymmetric ligands for catalytic asymmetric reaction. This book reviews research done in the study of pinacol coupling, including recent applications of ultrasound in pinacol coupling reactions.