Preheat the oven to 400 degrees F.
Toss the asparagus with the olive oil, garlic and rosemary, and sprinkle with salt and pepper. Separate the spears into piles of 3 or 4. Wrap a slice of bacon around each pile, spreading out the bacon as you go so just the top and bottom of the spears are showing. Place the bundles on a baking sheet and bake until the bacon is cooked through, 20 to 25 minutes.