The combination of solid-phase peptide synthesis (SPPS) with chemoselective ligation reactions enables the chemical synthesis of uniquely modified proteins. Of the chemoselective ligation strategies available, the Kent group's native chemical ligation (NCL) has proven to be highly robust and is widely used in the chemical synthesis of proteins. With NCL, peptide segments bearing an N-terminal Cys and C-terminal thioester can be chemoselectively ligated to generate synthetic proteins. NCL has been extended beyond Cys junctions via free-radical desulfurization, a robust technique that allows the more common Ala, as well as other amino acids amenable to thiol surrogates, to be used as ligation junctions. NCL has produced many useful synthetic proteins, including targets for mirror-image drug discovery, functional native and mirror-image enzymes, mirror-image proteins for racemic crystallography, and proteins containing complex post-translational modifications. However, NCL has several challenges that limit its scope in chemical protein synthesis (CPS). First, NCL requires high peptide concentrations, typically ≥ 1 mM, at neutral pH for efficient ligation. Unfortunately, peptide segments are often too insoluble to reach these ideal concentrations, even in denaturing conditions. While many groups have developed strategies to increase peptide solubility, these do not overcome the inherent issue of requiring high concentrations. Additionally, the availability of suitable Cys or Ala ligation junctions is limited for many synthesis projects, forcing the selection of suboptimal segments for NCL. Although alternative thiolcontaining amino acids, such as penicillamine (thiol derivative of Val), can be used as junctions to increase access to alternative ligation strategies, these often suffer from slow ligation rates. In cases where limited suitable junctions exist, the use of sterically hindered thioesters may be required (e.g., Thr, Ile, and Val). Even under ideal NCL conditions, sterically hindered thioesters suffer from long reaction times that often result in loss of peptide because of competing side reactions, creating complex HPLC purifications that further lower yields. The NCL rate is also dependent on the type of thioester used. Most commonly, 4-mercaptophenylacetic acid (MPAA) is used for NCL due to its favorable transthioesterification kinetics. However, MPAA has several disadvantages, including strong near-UV absorbance and potential co-elution with products in RP-HPLC. Several alternatives can be used in place of MPAA to avoid coelution with peptide, though at the cost of slower NCL kinetics. Templated ligation strategies can overcome these major barriers by increasing the proximity of the reactive partners, the C-terminal thioester and the N-terminal thiol, thereby increasing their effective concentration (Scheme 1A). Templated ligations occur in an intramolecular fashion, converting reaction kinetics from 2 nd to 1 st order. An early example of such a proximity-driven reaction was demonstrated with Kemp's thiol capture. Effectively, templated ligations are macrocyclization reactions, a strategy commonly found in the synthesis of cyclic natural products and other compounds. Importantly, application of this strategy can improve the efficiency of slow thioesters and enable ligations at dramatically lower peptide concentrations, especially helpful for poorly soluble peptides.