Progress in Heterocyclic Chemistry: Volume 34, the latest in this annual review series commissioned by the International Society of Heterocyclic Chemistry (ISHC), contains both highlights of the previous year’s literature on heterocyclic chemistry and articles on new developing topics of particular interest to heterocyclic chemists. Highlight chapters in Volume 34 are all written by leading researchers in their field, thus constituting a systematic survey of the important original material reported in the literature of heterocyclic chemistry in 2021. As with previous volumes in the series, Volume 34 will enable academic and industrial chemists and advanced students to keep abreast of developments in heterocyclic chemistry in a convenient way.