Abstract: The present disclosure provides Cas9 variants, and base editors comprising these variants, that recognize non-canonical protospacer adjacent motifs (PAMs) and have less restrictive PAM requirements for editing. The present disclosure provides Cas9 protein variants comprising one or more amino acid substitutions relative to wild-type Nme2Cas9. Fusion proteins comprising the Cas protein variants described herein are also provided by the present disclosure. Further provided herein are methods for editing a target nucleic acid using the Cas variants and fusion proteins provided herein. The present disclosure also provides guide RNAs, complexes, polynucleotides, cells, kits, and pharmaceutical compositions. Further described herein are phage-assisted continuous evolution (PACE) systems, vectors, methods, and devices.