Transformations using organometallic complexes have played a central role in modern organic synthesis. The types of reactions based on organometallic complexes can be divided broadly into two categories: one is utilization of the complex as a carbanion source which is mainly applied to reactions using elemental metal complexes, and the other is based on late transition metal behavior such as coordination of a carbon-carbon multiple bond, oxidative addition, reductive elimination,-hydride elimination, or an addition reaction. Early transition metal complexes show both types of reactivity, and thus, in addition to their utility either as a carbanion source or as a synthetic reagent based on transition metal behavior, it is possible to utilize them for synthetic transformations based on the characteristic features of both types of reactivity. Group 4 early transition metal complexes are not exceptional, and their application in organic syntheses has continuously attracted much interest. Among them, reactions using organotitaniums and-zirconiums have been most extensively investigated. 1 This review surveys synthetic reactions starting from substrates having a carbon-carbon unsaturated bond such as olefins, conjugated dienes, or acetylenes where both characteristic reactivities of titanium mentioned above are used in tandem. The reaction involves, fundamentally, the generation of alkene-or alkyne-titanium complexes through the coordination of the carboncarbon multiple bond to a titanium complex, which is a characteristic feature of transition metal behavior, and their use as a carbanion source directly or