The use oflasers has entered almost every facet of medicine and biology. Therefore, it is to be expected that the reviews contained in this vol urne will reflect this diversity. As dinical acceptance has grown with various diagnostic and therapeutic applications, so has the need for a more thorough understanding of the theoretical background for each. This is especially true where a correlation is to be made between the theoretical background and the experimental data. It is only in this way that we can attain the optimal form of any therapy. The basic coupling ofenergy into biological tissue and its conversion into heat is characterized by many parameters. One ofthe most important is pulse duration. The review by Bimgruber in Chapter 6 shows how our knowledge ofthis parameter has been extended.The need for a more basic understanding of the interaction of electromagnetic energy with various kinds of materials has led to investigations on the nature of plasmas their stability and instability,and how theyexist. Docchio reviews the factors that cause them to occur at a specific locale and then to move away from that site. The availabilityofmany types ofoptical fibers has extended our ability to deliver laser energy from various types oflasers into almost anyselected location. This is particularly useful in medicine, where less invasive ap proaches to surgery and diagnosis are always helpful. However, as Rol and his colleagues explain, the power-handling capabilities ofoptical fibers limit many applications, particularly for short-duration, high-peak-power laser pulses.