Bilibin's work comes from Russian Fairy tales. The image above is from Fenist the Falcon, here is another image from that story. This guy was like the Russian Mucha, awesome.
I love the way that he uses the decorative borders as small illustrations within the larger. This image comes from the story Marya Morevna, here Tsarevich Ivan and Marya Morevna are fleeing from Koshchei the Deathless. He creates such a sense of light in the background.
These two come from The Frog Princess, which features some of Russian folk tales most prominent characters, Prince Ivan, Baba-Yaga, and Vasilisa the Wise. I especially love the very goofy looking old Tsar, see the bottom image.