If resources for HIV prevention efforts were truly unlimited, then this book would be en- tirely unnecessary. In a world with limitless support for HIV prevention activities, one would simply implement all effective (or potentially effective) programs without regard to expense. We would do everything useful to prevent the further spread of the virus that has already claimed hundreds of thousands of lives in the United States and millions of lives worldwide. Unfortunately, funding for HIV prevention programs is limited. Even though the amount of available funding may seem quite large...