From the Preface: The history of modern science is not merely a chronological narrative of scientific ideas, their turns, trends and inventors but also a record of the scientific methodology, theoretical and experimental, that has shaped them into a veritable knowledge-system. The origins of modern science and its methodology can be traced to the new mood (15th-16th cent.) which emerged in Europe, when the ancient speculative ideas about matter, motion, space and time began to be questioned; and the new concepts with their mathematical-physical approach laid a solid foundation for understanding the natural phenomena, both celestial and terrestrial. Over the past five centuries, modern science has made remarkable progress and earned the distinction of being the greatest intellectual enterprise of mankind today. Significantly, this new knowledge-system which has the appellation of Modern Science, has been unique in the sense that, unlike the other knowledge-systems, it has transcended the constraining barriers of region, religion, race, color and creed. Its applications, which are generally known as technology, have been enormously beneficial to the enrichment of our material life in a manner that no other knowledge-system has been capable of accomplishing it so far. The advent of the methodology-oriented modern science was not in the nature of a bolt from the blue. It had before it a broad spectrum of knowledge relating to astronomy, mathematics, medicine, and the physical and biological world, generated and fostered over the millennia by ancient cultures-Egyptian, Mesopotamian, Indian, Chinese, Greek and Islamic-each in its own way. Generally called the traditional sciences, their approach to the natural phenomena was influenced in one form or the other by the religio-philosophical ideas and practices as well as the cultural compulsions. For this reason and also because of the perceptible characteristics by which the traditional science of one region can be differentiated from that of the other, they are recognized by their geographical nomenclature like, Egyptian, Greek, Indian or Chinese astronomy, mathematics and medicine. Dr Baldev Raj, the dynamic and eminent Director of the National Institute for Advanced Studies and an eminent nuclear scientist who was very much interested in developing and offering courses for college- lecturers as well as several scientist-friends of mine who had read my earlier book titled: Modern Science: A Historical and Social Perspective, suggested, that I should try to prepare an educative, Resource-Book on history of science, which could help not only in charting out a course on history of science for the under- graduate-level students but also a book in the nature of a general reader on the history of scientific ideas from early times to the present. I have made an attempt to prepare one under the title: Landmarks in Science: A Historical Perspective, expanding, and modifying the material of the two chapters as well as some passages of the former book (the copyright of which rests with me as its author), and also adding new ideas and their exposition at several places. As the title indicates, this book, besides presenting briefly a profile of traditional sciences (with a little more details about Indian scientific heritage), provides a perspective on the major ideas of modem science, from the time of Renaissance in Science to the end of the twentieth century. It has confined itself to the ideas relating to physics, astronomy, chemistry, biology and geology, in a historical mould, like the other books on history of science normally do. However, the historically presented scientific ideas in its 14 Sections may be of help in developing a semester course for PU/ under- graduate students, with some additional inputs, wherever necessary, from the Faculty desirous of teaching history of science in their institutions. The importance of lectures with appropriate illustrations as teaching aids can hardly be overemphasized. Such illustrations (photographs and diagrams) can be found in internet and in the published catalogues and other publications of the History of Science Museum, Oxford; Science Museum, London; Douches Museum in Munich; and Smithsonian Institution, Washington. It is my fond hope that the history of science which is an inter-disciplinary subject of sound educational value in the modern context, will soon find its place on the educational canvas of at least some Universities, IITs and the Indian Institutes of Science Education and Research.