Induction-compatible cookware contains ferromagnetic materials – in other words, it contains iron, or has a layer with magnetic properties. Cast iron, enamel cast iron and most types of stainless steel cookware are all induction compatible (But not all types – for instance, All-Clad's MC2 line, which is made of aluminum and stainless steel, is not induction compatible).
Aluminum, copper or glass cookware will not work unless they have a layer on the bottom with magnetic properties.
To tell if a pot or pan is induction-compatible, hold a magnet to the bottom. If it clings, the cookware will work on an induction cooktop. Also, many manufacturers have started putting a n "induction compatible" symbol on the bottom of their cookware or they'll note compatibility on their packaging. The symbol often looks like a horizontal zig-zag or a coil.
If you have an induction cooktop, but a favorite piece of cookware doesn't work on it, don't fret – Mauviel makes a product called the Mauviel Induction Disc (Compare Prices), which can be placed on the cooktop under the pan; the heating reaction will then heat the contents of the pan.
