RNA modification in the form of N -methyladenosine (m A) regulates nearly all the post-transcriptional processes. The asymmetric m A deposition suggests that regional methylation may have distinct functional consequences. However, current RNA biology tools do not distinguish the contribution of individual m A modifications. Here we report the development of 'm A editing', a powerful approach that enables m A installation and erasure from cellular RNAs without changing the primary sequence. We engineered fusions of CRISPR-Cas9 and a single-chain m A methyltransferase that can be programmed with a guide RNA. The resultant m A 'writers' allow functional comparison of single site methylation in different messenger RNA regions. We further engineered m A 'erasers' by fusing CRISPR-Cas9 with ALKBH5 or FTO to achieve site-specific demethylation of RNAs. The development of programmable m A editing not only expands the scope of RNA engineering, but also facilitates mechanistic understanding of epitranscriptome.