This paper addresses the question of what the heart (or the “nature”) of science is. After a short introduction, I will first make a few preliminary historical and systematic remarks. Next, in answering the main question, I shall propose the following thesis: Scientific knowledge is primarily distinguished from other forms of knowledge, especially from everyday knowledge, by being more systematic. This thesis has to be qualified, clarified, developed and justified. In particular, I will develop the thesis in nine dimensions in which it is claimed that science is more systematic than everyday knowledge: regarding descriptions, explanations, predictions, the defense of knowledge claims, critical discourse, epistemic connectedness, an ideal of completeness, knowledge generation and the structure and representation of knowledge. Finally, I will compare my answer with alternative answers.