Jerzy Plebański (1928–2005) was a Polish theoretical physicist best known for his extensive research into general relativity, nonlinear electrodynamics and mathematical physics. He split his time between Warsaw, Poland, and Mexico, his permanent residence from the mid-1970s onwards. He is remembered, among other things, for defining the algebraic classification of the tensor of matter, for finding new solutions of the Einstein equations (for example, the Plebański–Demiański metric), formulation of the heavenly equations and the effective field theory relating GR and supergravity, known as Plebański action. The first part of the book is developed from Plebański's lecture notes. Andrzej Krasiński is Emeritus Professor at the Nicolaus Copernicus Astronomical Center, Polish Academy of Sciences in Warsaw. He served for many years on the Editorial Board of the journal 'General Relativity and Gravitation' and has acted as Poland's elected representative on the international committee of the International Society for General Relativity and Gravitation. He is author of Inhomogeneous Cosmological Models (Cambridge, 1997), co-author of Structures in the Universe by Exact Methods (Cambridge, 2009), and co-editor of Golden Oldies in General Relativity (Springer, 2013). His research record includes many papers on the interpretation of inhomogeneous cosmological models. He is also a co-author of a computer program, Ortocartan, for algebraic calculations in general relativity.