I just heard from a friend the other day that Resolve carpet cleaner works well on grout. In the past, I've used a bleach pen from time to time but it is a pain to do. My DH mentioned that the carpet cleaners are now offering grout cleaning services...if we had more space to do, I'd probably go that route. For now, it's just in our bathrooms. Vinegar & baking soda paste is another way if you have a firm brush.