Many of the synthetic methods developed to cyclise peptides take inspiration from nature and utilise the canonical residues, cysteine (Cys) and lysine (Lys), or the native N-and C-terminal functionality to form disulfide, thioether, and amide bonds. Cyclisation via amide bond formation has been applied using both synthetic methods (peptide ligation ) and biological approaches exploiting intein chemistry (e.g., SICLOPPS ), mRNA display, and ligase enzymes. Due to the nucleophilicity of the thiol sidechain, numerous Cys-selective reactions (beyond disulfide and thioether formation) have been developed/repurposed for peptide cyclisation. These include the formation of bicycles via alkylating scaffolds, bridging Cys residues using perfluoroaryl braces/fluorine displacement (and alternative bridging groups ), thiol coordination to bismuth, thiol-addition chemistry, and desulfurative replacement of a disulfide bridge. Incorporation of non-standard amino acids enables the exploitation of chemoselective (bioorthogonal) chemistry such as azide-alkyne cycloaddition (i.e., 'Click Chemistry'), Staudinger ligation and azide-phosphonite chemistry. Simple imine and oxime bond formation has been utilized, as well as more complex transition metal (TM)-catalyzed and multi-component chemistry. Radical reactions such as thiol-ene and, more recently, decarboxylative photoredox catalysis and C-H alkylation have also been successfully applied. Among this broad range of available synthetic techniques, Grubbs' ruthenium (Ru)-catalyzed ring-closing olefin metathesis (RCM) 48 reaction, in particular, has found extensive application as a method for peptide cyclisation due to effective formation of a proteolytic, hydrolytic, and redox-stable hydrocarbon linkage. Whilst an undeniably powerful method, RCM is usually conducted on protected peptides in organic solvent, and access to the saturated hydrocarbon necessitates reduction under harsh conditions. New, operationally simple techniques that retain the benefits of RCM, but that work effectively in more sustainable solvents, would offer an impactful alternative to this universally popular method.