Techniques of nondestructive testing of concrete have always interested materials engineers. One such way is with a concrete test hammer designed in 1948 by the Swiss engineer, Ernst Schmidt. This concrete test hammer makes use of the impact principle. The rebound of the impacting body is a function of the elasticity of the two bodies involved and of the initial momentum. The impact reading has been correlated to the compressive strength of concrete. While the test hammer does not provide the consistent results obtainable form carefully performed cylinder test, it gives excellent results as a trouble shooting instrument and also as a means of checking strength growth in concrete before removing forms or shoring. It appears to be one of the best methods yet devised for investigating the strength of concrete in a structure at low cost and without damage to the structure.