In the now extensive literature on general relativity and its related subjects, references abound to “known solutions” or even “well-known solutions” of Einstein's field equations. Yet, apart from a few familiar space-times, such as those of Schwarzschild, Kerr and Friedmann, often little more is widely known about such solutions than that they exist and can be expressed in terms of a particular line element using some standard coordinate system.

With the most welcome publication of the second edition of the “exact solutions” book of Stephani et al. (2003), an amazing number of solutions, and even families of solutions, have been identified and classified. This is of enormous benefit. However, when it comes to understanding the physical meaning of these solutions, the situation is much less satisfactory – even for some of the most fundamental ones.

Of course, there are now many excellent textbooks on general relativity which present the subject in a coherent way to students with a variety of primary interests. These always describe the basic properties of the Schwarzschild solution and usually a few others as well. Yet, beyond these, when trying to find out what is known about any particular exact solution, there is normally still no alternative to searching through original papers dating back many years and published in journals that are often not available locally or freely available on the internet. Proceeding in this way, it is possible to miss significant contributions or to repeat errors or unhelpful emphases.