Onion powder is dehydrated, ground onion that is commonly used as a seasoning. It is a common ingredient in seasoned salt and spice mixes, such as beau monde seasoning. Some varieties are prepared using toasted onion. White, yellow and red onions may be used. Onion powder is a commercially prepared food product that has several culinary uses. Onion powder can also be homemade.

Onion salt is a spice preparation using dried onion and salt as primary ingredients.

Commercial onion powders are prepared using dehydration, freeze-drying, vacuum-shelf drying and flow drying.Some commercial onion powders are irradiated as treatment against potential microbial contamination. It readily absorbs water upon contact, so commercial varieties may be packaged in airtight containers with a liner atop the container. Onion powder with a moisture content of 4–5 percent is prone to caking when stored in warmer environments, with increased temperatures corresponding to a shorter time for the occurrence of caking. Of general acceptance is that commercial onion powder is around ten times stronger in flavor compared to fresh onion.

Onion powder may be used as a seasoning atop a variety of foods and dishes, such as pasta, pizza, and grilled chicken. It is also a primary ingredient in beau monde seasoning. It is also sometimes used as a meat rub.  Onion powder is also an ingredient in some commercially prepared foods, such as sauces, soups, and salad dressings. It can also be used in many other recipes such as burgers or meatloaf.

Onion salt is used as a seasoning atop finished dishes and as an ingredient in many types of dishes, such as meat and vegetable dishes, casseroles and soups.