Abstract: This invention pertains to the use of a novel set of tags for the immobilization and/or purification of proteins or other biological or organic molecules. The invention provides troponin C, troponin C binding peptide, and troponin I, or active fragments or analogues thereof as convenient tags and affinity ligands for immobilizing, attaching, or purifying proteins or other molecules. Methods for producing troponin-tagged molecules, such as recombinant fusion proteins, are described. Methods for preparing a troponin affinity matrix that is capable of specifically binding its cognate ligand in the presence of calcium, and methods for using such a matrix to purify troponin-tagged molecules are also described.