In 1924, Hans Spemann and Hilde Mangold reported that a small collection of cells taken from a gastrulating newt embryo could, when transplanted into a separate embryo, coax the newly adjacent cells to form a second embryonic axis (1). This collection of embryonic cells came to be called the “organizer,” and its identification codified the concept of induction—that cells influence their neighbors to change fate, often in dramatic fashion. Importantly, the organizer does not actually “organize” the embryo; rather, it initiates a cascade of sequential induction events that ultimately give the embryo its shape. In the decades since this landmark observation, it has become clear that induction plays a ubiquitous role in both embryonic and adult tissues, and that secreted and/or membrane-associated factors mediate the process. How does the embryonic organizer model apply to the various features of malignant progression, including stroma formation, metastatic spread, and tumor heterogeneity?