Rucksacks are durable packs, secured by shoulder straps and, in some cases, a hip strap, and are used to carry supplies or other contents on one's back. Europeans commonly refer to backpacks as rucksacks; other common names include knapsacks, haversacks, or packsacks.

Rucksacks are useful for carrying heavy loads for prolonged periods. The pack's design balances the weight of the load on the shoulders, which are stronger than the hands. The use of a padded hip belt distributes the weight onto the hips, which are even stronger than the shoulders.

Rucksacks are popular with campers, climbers, hikers, bikers, skiers, snowboarders and other outdoor enthusiasts. For soldiers, rucksacks might contain a parachute or other life-support devices. Backpacks have also become popular for everyday activities like shopping, sightseeing and toting school books.

Rucksacks typically contain various features which include multiple cargo pockets, clips, loops, and webbing. Mesh pockets are useful for storing wet clothing, water bottles and snacks, and guide books. Sealed pockets can hold more delicate items like glasses, cameras or global positioning system (GPS) equipment. Bungee cords can be used to attach larger items like sleeping bags, skis, or snowboards to the outside of rucksacks.

Most rucksacks are made of nylon due to its strength and durability. Many are waterproof, adjustable, and have detachable compartments, quick-release closures, and a waist strap. Some packs contain compartments for MP3 players, headphones, and/or a walking pole holder.

Hydration packs are a popular feature of rucksacks that bikers and other outdoor users look for. A hydration pack supplies water from a reservoir, which is transported to the wearer through a hose.

Fit and capacity should be of primary concern when choosing rucksacks. Torso length determines the proper fit. The quantity and type of supplies you will carry determine the needed capacity. For lengthy trips and heavy loads, look for a backpack with an internal or external frame.