This study examined the contribution of word decoding, first-language (L1) and second-language (L2) vocabulary and prior topic knowledge to L2 reading comprehension. For measuring reading comprehension we employed two different reading tasks: Woodcock Passage Comprehension and a researcher-developed content-area reading assignment (the Global Warming Test) consisting of multiple lengthy texts. The sample included 67 language-minority students (native Urdu or native Turkish speakers) from 21 different fifth grade classrooms in Norway. Multiple regression analyses revealed that word decoding and different facets of L2 vocabulary explained most of the variance in Woodcock Passage Comprehension, but a smaller proportion of variance in the Global Warming Test. For the Global Warming Test, prior topic knowledge was the most influential predictor. Furthermore, L2 vocabulary depth appeared to moderate the contribution of prior topic knowledge to the Global Warming Test in this sample of language minority students. (Contains 3 tables, 1 figure, and 2 footnotes.)