Regulation of contraction in skeletal and cardiac muscle occurs through calcium binding to the protein troponin C (TnC). The N‐terminal domain of TnC (NTnC) carries out the regulatory role through the binding of calcium ions – two calcium ions in skeletal muscle and one in cardiac muscle. Thirty‐nine sequences of TnC have been sequenced so far. Of the 39 sequences of TnC, 5 have had their three‐dimensional structures determined in various forms by NMR and X‐ray. Available structures include 26 uncomplexed structures in various calcium states, and 13 structures in which cardiac and skeletal TnC is complexed with fragments of troponin I and/or troponin T.