Can painters paint over wallpaper or do I need to strip it first?

Stripping is standard practice and strongly recommended for any wallpaper. Painting directly over wallpaper risks seam bubbling within 6 months, peeling at seams, and telegraphing of patterned designs through the paint. If you must paint over wallpaper (e.g., the wallpaper is glued tight to drywall paper face), prep with an oil-based primer (Zinsser BIN or Gardz) to lock seams, skim coat over visible seams with joint compound, sand smooth, and only then paint. Total cost typically still runs 70–85% of strip + paint, and the result is materially worse. Strip if at all possible.