Muesli (müsli in German or birchermüesli in Switzerland, pronounced ['mju:z li]) is a healthful high-energy breakfast cereal which contains mainly uncooked rolled oats, along with dried or fresh fruit, nuts, seeds, honey, spices, or chocolate. It is usually served with milk, yoghurt, or cream. Other varieties also exist.

Muesli was invented in 1900 by Swiss doctor Maximilian Bircher-Benner for patients in his hospital. Initially, the cereal contained grated apple, lemon juice, milk, and nuts, and was provided with the daily breakfast as a protection from illnesses of all kinds.

Although Bircher-Benner's recipe was never licensed, the idea spread quickly. While modern muesli has little in common with the original, it remains associated with good health.

Modern producers sell a wide variety of pre-packaged muesli, although the ingredients vary significantly between products. Some consumers prefer to mix their muesli themselves from fresh ingredients and to their own individual taste.