This week's set of six hard puzzles (rated SE 2.5–3.4). A new set appears every Monday. Fold the page in half for two sittings, or hand three puzzles to a rival and race.
Other difficulties: Easy · Medium · Expert — or try the daily print sudoku.
Stuck on one of these? The Sudoku Academy walks through every solving technique from naked singles to forcing chains, with examples pulled from real games.