Jeremy Gray is Professor of the History of Mathematics and Director of the Centre for the History of the Mathematical Sciences at the Open University, and a regular Visiting Professor at the University of Warwick. He works on the history of mathematics in the 19th and 20th Centuries, and also on issues in the philosophy and social significance of mathematics. He wrote 'The Hilbert Challenge', Oxford University Press, 2000, and he was the editor of and a contributor to 'The Symbolic Universe: geometry and physics, 1890-1930', Oxford University Press, 1999. His book 'Janos Bolyai, non-Euclidean geometry, and Nature of Space', a Burndy Library publication, MIT, came out in 2004. José Ferreirós is 'profesor titular' for Logic and Philosophy of Science at the University of Seville. He is the author of 'Labyrinth of Thought: A history of set theory and its role in modern mathematics', Basel, Birkhäuser, 1999, 'Science Networks' no. 23. He has edited in Spanish 'Riemanniana Selecta' (Madrid, CSIC, 2000, bilingual edition) and Dedekind's foundational works (Madrid, Alianza Editorial, 1997), and has published papers on the history and philosophy of logic, mathematics, and general science in journals such as 'The Bulletin of Symbolic Logic', 'Historia Mathematica', 'Archive for History of Exact Sciences', 'Science in Context', 'Theoria' and 'Critíca'. Among his forthcoming papers are contributions to 'Landmarks in Western Mathematics' (Elsevier), 'The Shaping of Arithmetic' (Springer), 'Filosofia de las ciencias matemáticas, naturales y sociales' (Trotta), and 'Philosophical insights into logic and mathematics' (Kluwer).