This paper provides an introduction to a unifying heterodox approach to the micro-macro link in economics. We emphasize the analytical problems that may arise from popular misunderstandings about the relationship of individual and aggregate level and thereby illustrate why a thorough understanding of aggregation and aggregates in science is necessary In a second step we show that the different heterodox approaches to the micro-macro link in economics are not only consistent, but complementary to each other and allow for a concise treatment of the micro-macro link based on a set of shared fundamental principles. We then argue that the central pillars of different heterodox conceptions of the micro-macro link can be subsumed under a common philosophical umbrella labeled 'systemism'. This umbrella is a useful device helping to explore the commonalities and differences in various heterodox approaches to the micro-macro link in economics. We argue that systemism can serve as a common denominator for the different approaches, enabling mutual communication and comparability.