One of the most famous inorganic polymers containing group 15 elements is poly(phosphazene)s. Phosphorus-containing organic–inorganic hybrid polymers show a variety of important properties for flame retardants, ionic-conducting materials, and easily separable supports for metal catalysts. Moreover, properties of the phosphorus-containing polymers can be tuned by changing the oxidation state or coordinating towards transition metals. More recently, several π-conjugated polymers featuring phosphorus atoms in the main chain have been reported and showed interesting features. Despite a plenty of phosphorus-containing polymers have been reported, arsenic-, antimony- and bismuth-containing polymers are still rare. In this chapter, homochain oligomers and polymers of...