The chapter covers mainly triaza- and tetraazamacrocyles and, among them, derivatives of cyclen and cyclam. The text presents cyclization procedures, protection strategies and further modifications of the azacycles. The main part is devoted to synthetic modification of the ring secondary amine groups with (coordinating) pendant arms. The azacycles mostly serves as complexation agents (ligands, chelators) and their properties are further modified and tuned through donor atoms present in these pendant arms. Ligands containing another reactive group are often conjugated to biological vectors and these bifunctional ligands are highlighted. The text also covers so-called cross-bridged macrocycles. Properties of the compounds in the solid state are demonstrated on selected examples. Finally, metal binding properties of the azacycles and applications of the complexes as MRI contrast agents, radiopharmaceuticals, luminescence probes and paramagnetic labels are briefly discussed.
