15cm forged carbon steel chef's knife with olivewood handle

A chef's knife, or cook's knife (sometimes referred to as a French knife) is a general kitchen knife and an absolutely indispensible tool for any chef or home cook. The all-purpose chef's knife has a broad, curved blade with a taper towards the tip. Its big cutting surface enables the user to cut small or large ingredients with enough leverage. It's probably the most essential and versatile of all kitchen tools and is designed to handle most cutting tasks.
If you could only have one knife, a good chef's knife is your best bet. Chef's knives usually range from about 15cm to 30 centimeters (8" to 16"), the most common size being 20cm (8"), although smaller and even larger cook's knives exist.

There are countless purposes for a chef's knife in the kitchen. Here are some common ones:

General cutting and chopping
Slicing and dicing vegetables, onions, fruits, meat and fish, chopping herbs, nuts, spices and whatever more. The long, curved blade allows for both rough and precise cutting, the height of the blade enables both the use of a guiding finger and the use of a chopping board, with the fingers that hold the handle high enough aboven the board to not get in the way. With proper knife technique (a bit of practice goes a long way), a chef's knife can be used for even cubes, and consistent strips (julienne).

Mincing and fine chopping
The curved edge or "belly" of a chef's knife facilitates a rocking motion, which is useful for (finely) chopping garlic, nuts, herbs, shallots and leaves. When chopping herbs or vegetables, the large size of the knife allows for chopping large quantities at once.

Slicing and carving
Although the best option for carving or slicing is a specialized carving knife or slicer, a chef's knife is an excellent alternative. It can be used to easily slice through cooked or uncooked meat, roasts, (big) pieces of fish or poultry, carving large chunks into smaller pieces or make thin, even slices. But do take into account that for slicing, a specialized carving knife with a long, thin and narrower blade with less friction is the optimal solution.

Crushing, smashing and bruising
Because of the broad blade and sturdy construction, the flat side of most chef's knives can be used for crushing garlic or ginger, lemongrass and other ingredients, for smashing nuts and seeds and bruising herbs and spices. This enables better flavor extraction or prepares ingredients for further processing.

Heavy-duty tasks
Tougher, more demanding cutting tasks, like cutting through bones, pumpkin, squash or certain frozen foods should not be attempted with a small, delicate knife, but can usually be achieved with a well-constructed chef's knife. And the longer the knife, the more leverage can be used. Obviously, certain tasks require a proper cleaver, which has a wider edge and a thicker blade. When in doubt, do not risk your beloved chef's knife.

Precision tasks
Even though a chef's knife is not as nimble and maneuverable as a paring knife, it can still be used for things like, trimming fat, deveining shrimp, removing skin from fish or meat and other controlled cuts.

Shredding
Leafy greens can easily be sliced and shredded with a chef's knife. The longer the blade, the bigger the pile of lettuce, cabbage, kale or spinach you can cut. The wide blade enables smooth and even cutting of such piles.

Scooping
When preparing ingredients on a cutting board or chopping block, the flat side of a chef's knife can easily be used as a scoop for transferring the cut ingredients to a pot or pan, or directly to a bowl or plate.

Sometimes the word French knife is used to describe a chef's knife, because of the long history of French culinary traditions and the broad influence of French cuisine (and its emphasis on technique, precision and quality kitchen tools) on professional cooking.