Corrosion is the principal reason for causing degradation of steel material properties, and coating is one of the most popular and effective ways to protect steel from corrosion. There are many kinds of coatings with different constituents, mechanisms and effectiveness. This paper presents a comprehensive review on the development of coating technology including traditional coatings, hydrophobic coatings, conducting polymer coatings and nanopolymer composite coatings. In particular, conducting polymers and nanopolymer composite coatings are reviewed in detail, which are the most popular and promising coatings. The advantages and limitations of each coating method as well as the influencing factors on corrosion protection are elaborated. Finally, the future research and applications are proposed.Coatings 2019, 9, 807 2 of 22 fluorocarbon coating, silicone coating, polyurethane coating and zinc-rich coating, provide corrosion protection by their barrier effect to ionic species, oxygen and water transport, which diminishes the corrosion rate [5][6][7], but their shortcomings are still significant, such as low impact strength, poor weatherability, poor bond strength and poor durability [8]. Almost all prevailing superhydrophobic coatings can adopt nanotechnology. Silica nanoparticles [9][10][11], carbon nanotubes [12,13], titanium oxide nanotubes [14][15][16][17], nanopolymers [18][19][20] and nanosilane [21][22][23] have been widely used for fabricating superhydrophobic coatings. Procedures such as the dip coating technique, electroless plating, sol-gel process and electro deposition are adopted to fabricate the superhydrophobic coatings. The water contact angles of the superhydrophobic coatings can reach 145-165 • C [9-23]. There is also some literature about using soft lithography method based on a polydimethylsiloxane (PDMS) template to prepare nanostructured superhydrophobic coatings [24,25]. Although significant progress has been achieved regarding the synthesis of superhydrophobic coatings and their anticorrosion properties for steel, the majority superhydrophobic coatings have been studied only in laboratory till now, and there are still many obstacles before they could be widely used in industry. The prevailing fabrications are complicated, costly and not suitable for on-site use. Many efforts should be made to develop an optimum superhydrophobic coating with excellent water repellency, long service life, good adhesion performance, low cost, easy fabrication and convenience in site spraying and curing.In recent years, conducting polymer coatings and nanopolymer composite coatings have been widely used in many projects. Many studies on nanopolymer composite coatings, conducting polymers and their combinations were conducted with a good deal of progress. Some new nontoxic corrosion protection materials with the properties of high efficiency and smart corrosion protection, long effective period and easy construction have been developed.Different coatings have deferent deposition mechanisms. At present, the prev...