The vast majority of bindings for Alpine skiing work by fixing the ski boot to the ski at the toe and heel. The binding attaches the boot to the ski, but to reduce injury also allows the boot to release in case of a fall. The boot is released by the binding if a certain amount of torque is applied (usually created by the weight of a falling skier). The amount of torque required to release the boot is adjusted by turning a screw on the toe and heel piece. This is called (colloquially) the DIN setting, because the standards for Alpine ski binding settings are issued by Deutsches Institut für Normung. The correct DIN setting is based on height, weight, ski boot sole length, the skiing style of the skier (cautious, average, or aggressive) and, age (if the skier is 50 years old or older). The DIN is usually set by a technician when skis are rented or bought. Ski service technicians and binding manufacturers recommend that bindings be adjusted and inspected by properly trained service technicians, because incorrectly adjusted bindings may release prematurely, or may fail to release, creating a potential hazard.
Bindings can be sold alone to be mounted to "flat" skis or can be integrated systems. While integrated systems generally provide a more natural flex, better power transmission, and a larger sweet spot, they also add more distance between the boot and the ski. While this is helpful in achieving higher edge angles, the high lift can strain the knees when skiing powder, and will make landings less stable. For this reason, most powder or freestyle skis are sold flat, while most carving and race skis come with an integrated binding system.
Alpine ski bindings employ the use of a snow brake to prevent the ski from moving while it is not attached to a boot. Snow brakes work by the use of a sprung square 'C' shape, typically made of metal, which makes contact with the snow. When a ski boot is put in the ski binding, the brake pivots under the downward pressure and runs parallel with the ski allowing free movement. When the boot comes out of the ski, the brakes spring out perpendicular to the ski and stop the ski from sliding.
There are three common Nordic binding systems:
Like Nordic bindings, Telemark bindings fix only the toe leaving the heel free to move. The main difference is that Telemark bindings are more heavy-duty to withstand the increased forces encountered in high speed descents. The cable binding (aka Kandahar binding), where the toe section of the boot is anchored, and an adjustable cable around the heel (for which there is a groove in the heel of the shoe) secures the boot. Used for cross-country (to a certain extent), Telemark and ski jumping.
While binding designs vary, before 2007 almost all dedicated Telemark models had been designed to fit boots with 75mm Nordic Norm "duckbill" toes. However, in late 2007 Rottefella introduced the New Telemark Norm (NTN) binding which uses a different boot sole, co-developed with the Crispi and Scarpa boot companies.
Also known as Randonee, an Alpine Touring ski is a special ski binding that allows the heel to be clipped down to the ski when skiing downhill, but which allows it to be released when climbing.
Traditionally, skiboards and Salomon's Snowblade have used non-release plate bindings. The reason being that skiboards and snowblades have traditionally been 100 cm in length or less, so the torque during a fall was assumed to be small enough that a releasable binding was not necessary. However, in recent years, as skiboarding has become a more established niche sport, releasable bindings have become a viable option to decrease the chances of injury. Spruce Ski created a riser which adapts between the standard 4 cm by 4 cm four-hole skiboard binding and standard ski bindings; furthermore, Spruce began selling their 120 cm skiboard in the 2005-06 season which are only available with their releasable setup. Additionally, Salomon now offers most of their Snowblades with releasable ski bindings as well. Many riders still prefer the plate-style bindings, and SnowJam and Bomber both make high quality plate bindings.