Phase analytical investigations in the system magnesium–iridium–indium revealed the magnesium-rich intermetallics Ir 3.30(1) Mg 17.96(4) In 0.74(4) and Ir 3 Mg 17.1(1) In 1.9(1) . The samples were prepared from the elements via induction melting in glassy carbon crucibles in a water-cooled sample chamber and subsequent annealing. Both intermetallics were investigated by X-ray powder and single-crystal diffraction: C2/c, Z=4, a=979.1(1), b=2197.4(2), c=848.2(1)pm, β=105.79(1)°, wR2=0.0434, 3076 F 2 values, 108 variables for Ir 3.30(1) Mg 17.96(4) In 0.74(4) , and a=983.39(8), b=2211.4(2), c=849.55(7)pm, β=105.757(6)°, wR2=0.0487, 3893 F 2 values, and 115 variables for Ir 3 Mg 17.1(1) In 1.9(1) . Both compounds show solid solutions. In Ir 3.30(1) Mg 17.96(4) In 0.74(4) , the indium site shows an occupancy by 69.9(4)% In+30.1(4)% Ir, and one magnesium site has a small mixed occupancy with indium, while nine atomic sites in Ir 3 Mg 17.1(1) In 1.9(1) show Mg/In mixing with indium occupancies between 1.2(3)% and 14.8(3)%. The relatively complex crystal structure is of a new type. It can be explained by a packing of coordination number 10 and 12 polyhedra around the iridium atoms. The crystal chemical peculiarities and chemical bonding in both intermetallics is briefly discussed.