Drilling is new test used to estimate the strength of in-situ concrete based on the drilling resistance measurements and a new designed non-destructive testing machine. This test includes three measured parameters: the drilling penetration rate, the pressure needed to drill a certain depth and the drilling rotational speed. It is an attempt to use the drilling penetration rate to estimate the strength of in situ concrete. The estimation of concrete strength using the drilling test measured parameters was expected to be more reliable than using the ordinary non-destructive tests to estimate the strength of concrete. In this Book, a new drilling machine was designed by considering all the factors that can affect the estimation of concrete strength. In addition, the rebound hammer and the ultrasonic pulse velocity tests were used to estimate the concrete strength for comparison with the new technique.