At the beginning of the 1990s research started in how to combine soft comput­ ing with reconfigurable hardware in a quite unique way. One of the methods that was developed has been called evolvable hardware. Thanks to evolution­ ary algorithms researchers have started to evolve electronic circuits routinely. A number of interesting circuits - with features unreachable by means of con­ ventional techniques - have been developed. Evolvable hardware is quite pop­ ular right now; more than fifty research groups are spread out over the world. Evolvable hardware has become a part of the curriculum at some universi­ ties. Evolvable hardware is being commercialized and there are specialized conferences devoted to evolvable hardware. On the other hand, surprisingly, we can feel the lack of a theoretical background and consistent design methodology in the area. Furthermore, it is quite difficult to implement really innovative and practically successful evolvable systems using contemporary digital reconfigurable technology.