In spite (or because) of its relentless progress, science is a perpetually unfinished work and so must be a description of any field of research at a given time. The first edition of this book tried to review the foundations and main achievements of the field that we called semiclassical string gravity covering the basics of general relativity, supergravity, and superstring theory aiming to provide a complete and self-consistent introduction to the effective field theory description and the black-hole and black-brane solutions of the latter (ten-dimensional supergravity and some of its compactifications). However, many interesting topics and results had to be omitted then due to lack of space and many others have emerged in the following years and I started feeling quite soon that the book was not complete and the goals I had set forth had not been reached.

Of course, for the aforementioned reasons, it is intrinsically impossible to give a complete and final description of this field in the absolute sense, but I think (the reader will be the judge) that the inclusion of a reasonable number of new topics was necessary and will make the book much more useful. The second edition is the result of trying to cover that necessity while preserving the self-consistency of the book by adding background and complementary material.

The two main gaps I have tried to close are the lack of a complete discussion of the black-hole attractor mechanism and a description of the classification/characterization of the supersymmetric solutions of general (matter-coupled) four-dimensional supergravities. These two subjects are linked by the original discovery of the attractor mechanism in supersymmetric extremal black-hole solutions of N = 2, d = 4 supergravity coupled to vector supermultiplets.

A self-consistent description of these two subjects has required, first, the addition of several new chapters (Chapters 6–8) on matter-coupled N = 1 to N = 8 four-dimensional supergravities, including detailed descriptions of the gaugings of the N = 1 and N = 2 theories.