The development of infrared (IR) and terahertz (THz) optical materials is work, that is connected with prospective applications in wide-spectral systems, medicine, IR and THz techniques. This work is focused on the development of new optical materials based on silver halides in the AgCl – AgBr – AgI system, selection of technological modes, preparation of single crystals and optical ceramics and investigation of their optical properties. The phase diagram of the AgCl – AgI system was refined, and a new phase diagram of AgCl – AgBr0.7I0.3 was investigated and constructed. In both diagrams, homogeneity and heterogeneity regions were found. In the AgCl – AgI diagram, the homogeneity region covers the concentration range from 0 to 7 mol. % AgI in AgCl, and the heterogeneity region from 7 to 98 mol. % AgI in AgCl. The phase diagram of AgCl – AgBr0.7I0.3 shows two regions of homogeneity in the concentration ranges of 0–49 and 78–100 mol. % AgBr0.7I0.3 in AgCl and one heterogeneous region from 47 to 87 mol. % AgBr0.7I0.3 in AgCl. In both systems in the regions of homogeneity it is possible to grow single crystals of the cubic NaCl crystal structure, space group Fm3m. For compositions of heterogeneous regions, it is possible to synthesize two-phase optical ceramics based on the cubic phase Fm3m and the hexagonal β-modification of AgI of wurtzite type (P63mc). The results of studies of phase diagrams of AgCl – AgI and AgCl – AgBr0.7I0.3 allowed us to determine the concentration ranges in the quasi three-component isothermal section of the AgCl – AgBr – AgI system. The obtained results allowed us to determine the compositions and select optimal technological modes, according to which single crystals of AgCl0.85Br0.10I0.05, AgCl0.72Br0.19I0.09, AgCl0.58Br0.29I0.13, AgCl0.97I0.03 and AgCl0.94I0.06 compositions were grown and optical ceramics of AgCl0.14Br0.60I0.26 composition were synthesized. The structure of the materials was determined by SEM analysis. The studied transmission ranges showed that single crystals and optical ceramics transmit radiation in the range from 0.48 to 41.7 μm and more with a maximum transparency level of up to 83 %. There are no absorption windows in the transmission spectra of the materials, which allows the developed optical materials to be used in the specified spectral ranges as transmission optics.