This chapter provides an overview of the accounts of scientific rationality and objectivity that have been offered by philosophers of science during the 20th century. We begin by presenting different accounts of how indi-vidual scientists should act to be rational an objective. In the latter half of the 20th century some philosophers argued that the rationality and objec-tivity of science is obtained at the level of communities of scientists ra-ther than at the level of individual scientists. Hence, we also present ac-counts of how communities of scientists, as opposed to individual scien-tists, can be rational and objective. We end the chapter by illustrating how the philosophical discussions about scientific objectivity may be rel-evant for scientific practice