The indium chalcogenides include all compounds of indium with the chalcogen elements, oxygen, sulfur, selenium and tellurium. (Polonium is excluded as little is known about its compounds with indium). The best characterised compounds are the In(III) and In(II) chalcogenides e.g. the sulfides In₂S₃ and InS.
This group of compounds has attracted a lot of research attention because they include semiconductors, photovoltaics and phase-change materials. In many applications indium chalcogenides are used as the basis of ternary and quaternary compounds such as indium tin oxide, ITO and copper indium gallium selenide, CIGS.
Some compounds that were reported and have found their way into text books have not been substantiated by later researchers. The list of compounds below shows compounds that have been reported, and those compounds that have not had their structure determined, or whose existence has not been confirmed by the latest structural investigations, are in italics.

There are a lot of compounds, the reason for this being that indium can be present as

• In³⁺ ,oxidation state +3
• In⁺, oxidation state +1
• In₂⁴⁺ units, oxidation state of +2, also found in some indium halides, e.g. In₂Br₃.
• non linear In₃⁵⁺ units isoelectronic with Hg₃²⁺.

The compound In₂Te₅ is a polytelluride containing the Te₃²⁻ unit.
None of the indium chalcogenides can be described simply as ionic in nature, they all involve a degree of covalent bonding. However in spite of this it is useful to formulate the compounds in ionic terms to get an insight into how the structures are built up. Compounds almost invariably have multiple polymorphs, that is they can crystallise in slightly different forms depending on either the method of production, or the substrate upon which they are deposited. Many of the compounds are made up of layers, and it is the different ways that the layers are stacked that is a cause of polymorphism.

In₂O, In₂Se

In₂O is well documented. It exists in the gaseous phase and there are numerous reports of small amounts detected in the solid phase but no definitive structure has been published. It is now believed that the compound described as In₂Se was actually a sample of In₄Se₃.

In₄S₃, In₄Se₃, In₄Te₃

In₄S₃ had been reported but has more recently been re-investigated and is now believed not to exist. Both In₄Se₃ and In₄Te₃ are similar black crystalline solids and have been formulated to contain a non linear In₃⁵⁺ unit that is isoelectronic with Hg₃²⁺. For example the selenide is formulated as In⁺ In₃⁵⁺ 3Se²⁻.In₄Te₃ und In₄Se₃: Neubestimmung der Kristallstrukturen, druckabhängiges Verhalten und eine Bemerkung zur Nichtexistenz von In₄S₃. U. Schwarz, H. Hillebrecht, H.J. Deiseroth, R. Walther Z. Krist. 210, 342-347 (1995)