This new reference, designed for both students and general readers, provides concise essays on more than one hundred basic core ideas or concepts in the natural and social sciences, supplemented by carefully selected bibliographic listings. Written with a minimum of technical jargon, the essays explore such issues as what it means to be "scientific," how theories related to facts in science, and how science compares with other intellectual disciplines. After presenting a clear explanation of the concept, each entry discusses the historical and intellectual context that gave rise to theoretical controversy and assesses the significance of the idea for both the particular discipline and science as a whole. The individual bibliographies will guide the student in tracing the historical development of each subject and investigating its scientific and philosophical aspects in greater detail. Cross referencing and subject indexing are supplied.