Wallpapering around a fireplace is the same as applying wallpaper around other obstacles, such as bookshelves or cabinets. It shouldn't take much longer than applying wallpaper over a flat wall, and all you need to get started is a razor knife, a small sharp pair of scissors, a pair of paperhanging scissors and a paperhanging brush.
Prepare the wallpaper
Cut the wallpaper roughly to size before you start applying it to the wall. This is done to ensure that you aren't left with lots of pasted paper after trimming. Leave a margin of about 2 inches; you will trim this later.
Paste the wallpaper
Hang the wallpaper as you normally would. When you get to the fireplace, mark its outline on the back of the wallpaper using your scissor blade. Peel the wallpaper back a little bit, and begin cutting along the outline. If the pattern of the fireplace is complex and requires many small cuts, use the smaller pair of scissors. If the fireplace is more straightforward, use the paperhanging scissors. If the paste begins to dry while you're cutting, apply more paste to the wall instead of the paper.
Smooth and clean the wallpaper
Paste the trimmed wallpaper back into place. Use the bristle points of the brush to smooth as needed when pushing the wallpaper into tight corners and spots. Don't forget to wipe off any glue before it dries.