The study of strigolactones (SLs) began in 1966 with the isolation of strigol from the root exudate of cotton (Gossypium hirsutum>) as a seed germination stimulant for the root parasitic plants, Striga spp. (Cook et al. 1966). Subsequently, SLs with a wide variety of structures have been isolated from various plant species. In 2005, It was found that the role of SLs exuded from host roots are symbiotic signals towards arbuscular mycorrhizal (AM) fungi that supply phosphate to host plants (Akiyama et al. 2005). Three years later, it was further discovered that SLs also function as a phytohormone that suppresses shoot branching in plants, thereby accelerating SL research (Gomez-Roldan et al. 2008; Umehara et al. 2008). Mutants with excessive shoot branching had been analyzed since the 1990s, and when they were found to be defective in SL biosynthetic enzymes and signaling components, the major biosynthetic and signaling pathways were elucidated in the last 15 years (Mashiguchi et al. 2021). In this special issue, young and mid-career researchers who will lead the next generation of SL research have provided four topics on new development in SL studies. Two of them are about the discovery of new physiological effects of SL as rhizosphere signals, and the other two are about the development of selective agents of various SL effects. I hope that these discoveries will attract more and more students and researchers to the ever-expanding fascination of the SL world.