Applications of in situ innovative remedial technologies are currently very promising, not only in Central and Eastern Europe but all over the world. In practice, in situ methods can be advantageous for cleaning up various types of contaminated site, but, of course, they have pros and cons. The remedial engineering measures can be optimized (no need to excavate or to pump), and, thus, the clean-up costs are also optimized, which is considered to be one of the main advantages of in situ technolgies. A major disadvantage is that in situ applications are always locally specific, and, therefore, it is necessary to evaluate site conditions thoroughly, and to assess the technical and financial feasibility before their use. Practical experience with in situ utilization of remediation technologies has shown that it is possible to create a general application methodology. In practice, this means that any application of an in situ remedial method should be carried out in the following five steps: (1) detailed investigation and evaluation of local site conditions; (2) selection of the best available in situ remedial technology; (3) laboratory testing of the chosen technology’s efficiency (bench-scale testing); (4) technology verification and its technical optimization (pilot/field-scale testing); and (5) practical application of the remediation method, including operation-checking control (full-scale application).