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Nine novel phosphates, based upon a combination of caesium, zirconium and lanthanide ions, were obtained from fluoride-containing fluxes using high-temperature crystallization. The structures of Cs1.80Eu0.80Zr1.20(PO4)3 (CsEuZrP), Cs1.79Gd0.79Zr1.21(PO4)3 (CsGdZrP), Cs1.87Tb0.87Zr1.13(PO4)3 (CsTbZrP), Cs1.67Dy0.67Zr1.33(PO4)3 (CsDyZrP), Cs1.75Ho0.75Zr1.25(PO4)3 (CsHoZrP), Cs1.78Er0.78Zr1.22(PO4)3 (CsErZrP), Cs1.70Tm0.70Zr1.30(PO4)3 (CsTmZrP), Cs1.52Yb0.52Zr1.48(PO4)3 (CsYbZrP) and Cs1.63Lu0.63Zr1.37(PO4)3 (CsLuZrP) were solved using single-crystal X-ray diffraction. All compounds are isostructural to the mineral langbeinite (cubic system, space group P213). Their framework structures originate from the cross-linking of metal octahedra [ MO6] ( M = Zr, Ln) by phosphate tetrahedra. Cs+ cations are located in the closed cavities of the framework and preferentially occupy one of the two available sites. The principles of crystallization of the equilibrium langbeinite-related phosphates in the fluxes of the system Cs2O–P2O5–LnF3–ZrF4 (Ln = La–Nd, Sm–Lu) are discussed based on their crystal structures. [ABSTRACT FROM AUTHOR]