Serious searches for signals from technological civilizations will be greatly enhanced by a new generation of radio telescopes, the first of which is currently under construction by the Radio Astronomy Laboratory at Berkeley. The probability that the searches will be successful depends, among many other things, on how commonly the conditions conducive to the development of life are found in the Milky Way. The birth of stars and planetary systems takes place in giant clouds of molecular gas and dust which are remarkably similar to one another throughout the Milky Way and in nearby galaxies. The sun-like stars that form within them inevitably have protoplanetary disks that have a large range in properties and are affected by environmental differences. If biological evolution requires catastrophic events such as bombardment by cosmic debris, the evidence suggests that although planetary systems vary greatly, such debris is common. Its distribution, and thus the likelihood of colliding with an earth-like planet, depends on the details of planet formation. Although the formation of earth-like sytems is probably not as common as previously thought, recent evidence suggests that the differences bewteen systems are less important than their similarities.