Our understanding of the ribonucleases that act to process and turn over RNA in Bacillus subtilis, a model Gram‐positive organism, has increased greatly in recent years. This chapter discusses characteristics of B. subtilis ribonucleases that have been shown to participate in messenger RNA maturation and decay. Distinct features of a recently discovered ribonuclease, RNase J1, are reviewed, and are put in the context of a mechanism for the mRNA decay process in B. subtilis that differs greatly from the classical model developed for E. coli. This chapter is divided according to three parts of an mRNA—5′ end, body, and 3′ end—that could theoretically serve as sites for initiation of decay. How 5′‐proximal elements affect mRNA half‐life, and especially how these elements interface with RNase J1, forms the basis for a set of “rules” that may be useful in predicting mRNA stability.