Although electroporation in the past has mainly been used as a research tool, recent work has demonstrated its potential for clinical applications. Some of the areas explored include electrochemotherapy (ECT), which utilizes electroporation as a means for delivering chemotherapeutic agents directly into tumor cells, encapsulation of drugs or genes into cells for their use as carrier systems, transdermal delivery of drugs or genes, gene therapy, and delivery of drugs or genes with an electroporation catheter. This article discusses the principles of ECT as a method of treating cancer, the requirements and development of electronic and electromechanical hardware for ECT, and it presents data for both in-vivo animal studies and clinical applications, especially for subcutaneous tumors. It is concluded that ECT has shown promise in treating a variety of cancers in humans. The basic principles are reasonably well understood. A good start has been made in the development of the necessary hardware to generate and apply the needed electric fields. As the human genome project progresses in identifying gene-based diseases and their possible cures, the same hardware system used for ECT can also be used for electrogene therapy. As ECT-based therapy becomes more widely recognized, it will offer an additional treatment modality and increased hope for cancer patients.