Corrosion of reinforcing steel in concrete is a serious problem from the point of view of both safety and economy. Therefore, it is essential to have reliable measurement techniques to evaluate the corrosion condition of the steel bars in the reinforcing concrete. Electrochemical assessment of the condition of the steel reinforced concrete structures is being carried out increasingly and more regularly, both in the laboratory and in the field. It is important to have enough information about the factors that may affect these measurements. In this way, results obtained from different tests can be interpreted in more reliable manner and the condition of the embedded reinforcing steel bars in concrete structures can be evaluated with more confidence. The main goals of this book are: i) to determine the causes of the errors in electrochemical measurements that may mislead the researchers, (ii) to determine factors that may affect the measurements, (iii) to attempt to manifest better interpretation of the results and (iv) to avoid the problematic pitfalls and overcome them as much as possible.