'This book gives a very careful analysis of the relation of theory to observational confirmation in astrophysics and cosmology, using as a case study the succession of MOND models proposed by Milgrom. Using Lakatos's approach, which is contrasted with Popper's proposals, the book focuses with exemplary clarity on the question of to what extent theories can be taken to be validated by observational tests. This is a great contribution to the philosophy of cosmology, which will also make the reader appreciate the strength of Milgrom's theory in terms of having, in advance, made predictions which were subsequently confirmed.' George F. R. Ellis, University of Cape Town