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We propose to study PDRs and dust in 5 low-metallicity regions: N159 and N214 in the LMC, N 27 in the SMC, and IC 10-SE in IC 10 using ISOCAM, ISOPHOT, and the LWS. The low-metallicity interstellar medium will have profoundly different properties than its higher metallicity counterpart in the Milky Way. Decreased dust shielding will produce larger photodissociation regions, because UV fields will penetrate much more deeply into the molecular clouds. The more intense UV fields will likely destroy the smaller dust grains, which will have important consequences on the shielding and the thermal balance in the metal-poor ISM. With the observations here proposed we will be able to: (1) determine the very small grain spatial distribution and temperature and their contribution to the heating-cooling balance, (2) determine the "classical" large grain spatial distribution and temperature and consequently the UV radiation shielding experienced by the gas phase of the ISM, (3) determine the emissivity index of the large grains, which will contain information about their size distribution and composition, (4) obtain an important set of FIR spectroscopic PDR diagnostics, in particular the 158 um [C II] and the 145 um and 63 um [O I] lines, and, (5) in conjunction with our submm [C I] and CO observations with the AST/RO telescope and existing KAO [C II] maps, we will obtain for the first time a complete set of PDR diagnostics for a number of low-metallicity systems as inputs and tests of PDR models.