The unity of science has been a widely discussed issue both in the philosophy of science and within several sciences. Reductionism has often been seen as the means of bringing the different sciences to a fundamental unity by reference to some basic science, but it shows many limitations. Multidisciplinarity and interdisciplinarity have also been proposed as methodologies for attaining unity without underestimating the diversity of the sciences.This volume starts with a clarification of the possible meanings of this unity and then discusses the features of the mentioned approaches to unity, evaluating the success and the shortcomings of the unification programme among different sciences and within a single science.