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We compared Snowy Owl feeding ecology from 15 breeding season studies throughout Nearctic and Palearctic circumpolar regions. We used raw data and information theory to assess the owls’ feeding niche. Combined studies yielded 59,923 prey items, of which 59,585 were used for calculations. Overall, mean food niche breadth (FNB) was narrow: H′ = 1.95; R = 1.60, D = 0.526. In 10 of 15 studies, lemmings were > 71.8% of the owls’ diet. In four studies, <i>Lemmus</i> was > 90% of the diet, and in three studies <i>Dicrostonyx</i> was >90% of the diet. In three other studies, <i>Lemmus</i> represented 71.8%, 73.8%, and 84.0% of the diet. In one study, <i>Lemmus</i> and <i>Dicrostonyx</i> were about equal: 49.1% and 47.5%. In the four remaining studies, <i>Microtus</i> and <i>Clethrionomys</i> voles were important. In contrast, of 5888 winter prey items from seven North American studies, the mean FNB (H′ = 4.61) was twice that of 15 breeding season scores, FNB (H’ = 1.95). The Snowy Owl is primarily an obligate lemming predator for breeding. Changes to population ecology and distribution of lemmings due to climate change will have direct affects and effects on the Snowy Owls’ reproductive output. The conservation of Snowy Owls is the conservation of lemmings.