The FASTK family proteins have recently emerged as key post-transcriptional regulators of mitochondrial gene expression. FASTK, the founding member and its homologs FASTKD1-5 are architecturally related RNA-binding proteins, each having a different function in the regulation of mitochondrial RNA biology, from mRNA processing and maturation to ribosome assembly and translation. In this review, we outline the structure, evolution and function of these FASTK proteins and discuss the individual role that each has in mitochondrial RNA biology. In addition, we highlight the aspects of FASTK research that still require more attention.