**1. Introduction**

The corrosion of metallic materials is one of the most common phenomena that cause problems and losses in billions of dollars annually in the industrial fields. In this context, several methods have been developed and applied to combat this phenomenon such as the use of corrosion inhibitors, cathodic protection, protective coating, and galvanization.

In recent decades, the use of the organic and inorganic corrosion inhibitors takes a great importance in the protection of metals against corrosion in various media. Generally, the mechanism of the action of these inhibitors consists to form an adsorptive protective layer on the metallic surface. Also, the adsorbed inhibitors can be connected to the metallic surface by means of chemical bonds (chemical adsorption) or physical forces (physical adsorption).

Recently, phosphonates and phosphonic acids are largely employed as effective corrosion inhibitors to protect metals against corrosion in various media [1–4]. Based on this, several pathways and procedures have been developed to prepare theses derivatives in good yields such as Michaelis–Arbuzov reaction [5, 6], Kabachnik–Fields reaction [7, 8], Pudovik reaction [9], Abramov reaction [10] and Moedritzer-Irani reaction [11]. In most cases these synthetic reactions require the use of a catalyst or, microwaves or ultrasounds in order to improve their yields and to minimize the reaction time [12–15].

Generally, the inhibition activity of organic and inorganic compounds can be studied experimentally using several chemical, electrochemical and microscopic methods such as weight loss measurements, polarization curves, electrochemical impedance spectroscopy (EIS), scanning electron microscopy (SEM), atomic force microscopy (AFM), infrared spectroscopy (IR), … etc. Moreover, the theoretical methods such as Density Functional Theory (DFT) and Molecular Dynamic Simulations (MDS) are effectively used in the field of corrosion inhibition. Generally, the DFT method can be used to correlate the experimental inhibition efficiencies with some structural and electronic parameters of the investigated inhibitors. On the other hand, the MDS are used to determine the adsorption modes of the inhibitive molecules on the metallic surface and calculating their adsorption energies.

The main objective of this chapter is to present of our published research results concerning the synthesis and the use of phosphonates and phosphonic acids as a new generation of corrosion inhibitors. All inhibitors and their anticorrosion results presented in this chapter are exclusively studied and provided by our research team in the Laboratory of Electrochemistry of Molecular Materials and Complex (LEMMC) at Ferhat ABBAS Setif-1 University, Algeria.
