The ideal condition for skiing is to have the skis perfectly flat on the snow. Since the ski boot is tightly secured to the ski, you can visualize how any tipping of the boot to the inside or outside will cause either the inside or the outside edge of the ski to lift off the snow. Most people have some degree of inherent tilt in the boot sole to kneecap range. That is to say, almost all of us are bowlegged or knockneed to some degree, though not necessarily in both legs. To make the ski lie flat without straining or while in a neutral stance we need to have the offending boot or boots canted opposite to the natural lean of the leg.
How would I know if I need canting?
Relative to skiing, the first person on the ski slope to notice if there is a misalignment in your stance would probably be a ski instructor. Instructors have seen so many skiers with stance problems that it is easily detected by a visual appraisal or by watching the bio-mechanics while you ski. If an instructor says you may need correction in your stance, believe him and have a reputable boot shop do an alignment check.
What does the canting process involve and where do I go?
Find a reputable boot fitting shop near you, or near a resort you frequent, because fine tuning your boot corrections can take several visits. The technicians or boot fitters at the shop will do an alignment procedure to determine how far, in degrees, the center of your knee mass is from a perpendicular line from the center of your boot. Once this difference is known then the technician can decide if you need your boot, or boots, canted to have your skis lay flat.
How much should I expect to pay for the whole process including canting if I need it?
In most cases the alignment procedure and any canting work will be included in the price if you have both done at the same place. Some shops will charge you nothing for an alignment check if you do not need canting work, but others may charge a fee if that's all the work you need done. If you have foot beds done, expect a free alignment check. The canting itself is either an angled build up of your boot sole or a shaving down of your boot depending on which procedure the shop offers. For canting expect to pay around $100 or more, depending on other boot work done.