Knowledge was a major issue in science and philosophy in the twentieth century. Its first irruption was in the heated controversy concerning the foundations of mathematics. To justify his rejection of the use of the actual infinite in mathematical reasoning, Brouwer has made the construction of mathematical objects dependent on the knowing subject. This approach was rejected by the mainstream of analytical philosophers who feared a fall into pyschologism. Several years later, the question of the progress of scientific knowledge was put forward in the thirties by the post-positivist philosophers to fill the vacuum in the philosophy of science following the demise of the logical positivism programme. The answers given to these questions have deepened the already existing gap between philosophy and the history and practice of science. While the positivists argued for a spontaneous, steady and continuous growth of scientific knowledge the post-positivists make a strong case for a fundamental discontinuity in the development of science which can only be explained by extrascientific factors. The political, social and cultural environment, the argument goes on, determine both the questions and the terms in which they should be answered. Accordingly, the sociological and historical interpretation involves in fact two kinds of discontinuity which are closely related: the discontinuity of science as such and the discontinuity of the more inclusive political and social context of its development. More precisely it explains the discontinuity of the former by the discontinuity of the latter subordinating in effect the history of science to the wider political and social history. The underlying idea is that each historical and social context generates scientific and philosophical questions of its own. From this point of view the question surrounding the nature of knowledge and its development are entirely new topics typical of the twentieth century social context reflecting both the level and the scale of the development of science. To the surprise of modern historians of science and philosophy, the same kind of questions, which would allegedly be new topics specific to the twentieth century concerning the nature of knowledge and its progress, were already raised more than eleven centuries earlier in the context of the Arabic tradition which, as we discuss further on, developed a trans-cultural and trans-national concept of the unity of science (see the contributions of Deborah Black and Jon McGinnis which tackle the issue of the nature of knowledge). The neglect of the Arabic tradition in philosophy of science is a major a gap not only in the development of science but a fundamental flaw in the writing of its history and philosophy caused by the total reduction of epistemology to political and social history of science. How has this period of the history of science and philosophy come to be ignored? In what circumstances were the questions akin to the nature of knowledge raised in the first place? What is the relation between on the one hand the questions of knowledge and its growth and on the other hand the unity of science in the Arabic tradition? The answers to some of these questions are the aim of the present volume, the first of the series Logic, Epistemology and the Unity of Science to be devoted to a so-called non-western tradition. Let us first highlight in a kind of overview some landmarks concerning the timing of the emergence of the Arabic tradition and its significance for the history of science.