NNN (New Nordic Norm)
The most typical type of cross-country ski binding, the New Nordic Norm, was developed by the Rottefella Company in 1985. The NNN bindings were improved upon in 1990. Old NNN boots are not compatible with the newer NNN bindings and new NNN boots do not work with old NNN bindings. NNN compatible boots have a metal rod on the bottom of the boot--at the front of the boot under the toes--that allows you to step into the binding. The rod catches the latch mechanism and locks in place. Some skis have two ridges on the surface that align with ridges on the soles of your boots, as well. To remove from the binding, lift your boots from the toes up toward your shin. NNN bindings can be found on standard cross-country skis as well as skate skis.
Salomon Nordic System Pilot (SNS)
Developed by the company Salomon and based on an idea from Bjørn Dæhlie, SNS binding uses two rods on compatible boots above the toes. The bars click into two different slots. SNS skis only have one ridge for alignment on the surface, as do the boots. With only one ridge, there is less stability but also less of a chance of icing up. To get in and out of the skis, you step into the binding and release by lifting the toes up, just like the NNN bindings. SNS bindings and boots are not compatible with NNN boots and bindings. Pilot boots will work with SNS Profil and Pilot bindings. These bindings are used for both skate skiing and classic cross-country skiing but have different designs for each. Salmon and Atomic are two brands that make this type of binding. This is the most expensive type of binding.
Salomon Nordic System Profil (SNS-P)
This type of binding is Salomon's newest binding and the standard SNS binding used. Unlike the Pilot, this binding only has one rod above the toes. There is still only one ridge that lines up from ski to boot. These bindings come in many different types from recreation to racing. They can be found on skate and cross-country skis. Profil boots only work with Profil bindings. These bindings are cheaper then the Pilot bindings.
NNN or SNS?
There is no real advantage of picking one system over the other. Start with picking out the right boot for you and then pick the matching binding from there. Boots are where you should spend the extra money, as they are what controls your skis.
Backcountry bindings come in both SNS and NNN versions. BC boots are the only boots that will work with BC designated bindings. You cannot mix between SNS BC and NNN BC versions. These systems are lightweight and have superior control for downhill and ungroomed terrain. Extra traction is added to the boots, and the bindings are more rugged for the conditions.