Iron and steel (alloy of iron) are most easily protected by paint which provides a barrier between the metal and air/water. Moving parts on machines can be protected by a water repellent oil or grease layer. Covering the surface with enamel and lacquers is another method.

Sacrificial Protection 

 'Rusting' can be prevented by connecting iron to a more reactive metal (e.g., zinc or magnesium). This is referred to as sacrificial protection or sacrificial corrosion, because the more reactive protecting metal is preferentially oxidized away, leaving the protected metal intact.

Alloying

 Iron or steel along with other metals can also be protected by 'alloying' or mixing with other metals (e.g., chromium) to make non-rusting alloys. Stainless steel is an example of a nonrusting alloy of iron and carbon. Brass, an alloy containing copper is another metal alloy which is less expensive and non-reactive.

Galvanizing 

Coating iron or steel with a thin zinc layer is called 'galvanizing'. This layer is produced by electrolytic deposition. Dipping the iron/steel object in molten zinc and using it as the negative cathode zinc is coated on it. Zinc preferentially corrodes or oxidizes to form a zinc oxide layer that does not flake off like iron oxide rust. Also, if the surface is scratched, the exposed zinc again corrodes before the iron and continues to protect it. 

Electroplating 

Coating the surface with metals like tin, chromium, nickel etc. by electroplating is also utilized to prevent corrosion. Steel cans are protected by relatively un-reacted tin and works well as long as the thin tin layer is complete.