\input zb-basic \input zb-ioport \iteman{io-port 05617723} \itemau{Kouck\'y, Michal} \itemti{Circuit complexity of regular languages.} \itemso{Theory Comput. Syst. 45, No. 4, 865-879 (2009).} \itemab Summary: We survey the current state of knowledge on the circuit complexity of regular languages and we prove that regular languages that are in $\text{AC}^{0}$ and $\text{ACC}^{0}$ are all computable by almost linear size circuits, extending the result of {\it A. K. Chandra, S. Fortune} and {\it R. Lipton} [J. Comput. Syst. Sci. 30, 222--234 (1985; Zbl 0604.68051)]. As a consequence we obtain that in order to separate $\text{ACC}^{0}$ from $\text{NC}^{1}$ it suffices to prove for some $\epsilon >0$ an $\Omega (n ^{1+\epsilon })$ lower bound on the size of $\text {ACC}^{0}$ circuits computing certain $\text{NC}^{1}$-complete functions. \itemrv{~} \itemcc{} \itemut{regular languages; circuit complexity; upper and lower bounds} \itemli{doi:10.1007/s00224-009-9180-z} \end