Transcription Activator-Like Effectors (TALEs) are bacterial virulence factors containing a domain of repeats that recognize specific DNA sequences and reprogram transcription activation of invaded plant cells. TALE genes encode 5 to 30 repeats with average pairwise repeat identities greater than 91%. Most variability arises from only two positions termed Repeat Variable Diresidues (RVDs), which confer DNA binding specificity. Crystal structures of free and DNA-bound TALEs (Deng et al. Science 2012) show a large conformational change upon DNA binding. Thus, DNA binding is likely coupled to the free energy of tertiary structural change between the TALE repeats. We are interested in quantifying this relationship and relating it to folding cooperativity using nearest-neighbor (“Ising”) models.To investigate the length dependence of folding, we created a set of consensus TALE constructs of varying length. Solubilizing N- and C-terminal caps are needed to favor monomeric protein in solution as detected by sedimentation velocity analytical ultracentrifugation. Capped consensus TALE repeat constructs have alpha-helical secondary structure as measured by farUV CD. Urea-induced unfolding transitions of TALE repeat arrays were measured and show cooperative unfolding transitions as well as increases in stability with length. These data are well-fitted by an Ising model, which separates the contributions of intrinsic and interfacial free energies. TALE repeats have an unfavorable intrinsic folding free energy of 5.3 kcal/mol and a favorable interfacial free energy of −6.8 kcal/mol. Using these values, the length dependence of TALE stability can be modeled, and shows TALEs under 5 repeats to be unfolded. Using the Ising parameters, we find that partially folded states with a single repeat unfolded are energetically accessible. Population of these partially folded states may be important for DNA binding.