In many scientific disciplines, political discussions, and social policy forums, there has been increasing interest in diversity as an inherent good. There is corresponding concern about sliding down a slippery slope to complete relativism with an accompanying loss of critical standards. In philosophy of science, this tension takes the form of a debate between defenders of the unity of science-those who advocate strong critical standards based on metaphysical and methodological monism-and supporters of the disunity of science-some of whom endorse forms of pluralism that verge on the brink of an `anything goes` leniency. In this research Mitchell explores a middle ground. The aim is to develop a pluralistic picture of scientific practice that retains critical standards of acceptability within science. The strategy adopted is two-pronged, focusing on both metaphysical questions and epistemological issues. Contemporary biology provides the location for exploring these topics and testing the results. The metaphysical investigation involves a comprehensive analysis of the metaphysics of complexity. Three forms of complexity are identified: complexity of structure, complexity of process, and complexity of evolved domains. In the epistemological part of the research, Mitchell clarifies the possibilities and constraints on representing scientific laws, models and explanations. Particular attention is paid to the idealized character of models, the need for integration of multiple models in explanation and the degrees of contingency symbolized in laws of nature. The framework of critical pluralism that will result from this work will provide three practical benefits: 1) it will allow one to distinguish between real and spurious scientific disputes; 2) it will offer a taxonomy of types of conflict; and 3) it will allow a better understanding of different kinds of compatibility and complementarity between alternate theories.