Although communicable disease (CD) and non-communicable disease (NCD) are often thought of as separate, competing entities particularly when it comes to funding pipelines and interventions, the two classes of disease are in fact intimately related. Medical anthropologists and sociologists have long recognized that social determinants such as poverty serve as a common breeding ground for CDs and NCDs, but the relationship between the two kinds of diseases can be even more direct. This article explores the intimate symbiosis between CDs and NCDs through a range of illustrative examples. In some CD-NCD pairs, the CD causes or is etiologically associated with an NCD, illustrating that NCD interventions are sometimes more effective when coupled with CD interventions, such as vaccination programs. In others, the relationship is better characterized as bidirectional, each worsening the outcomes of the other. From a broader perspective, these relationships also connect with each other in a larger web of various CD-NCD interactions. Because of these reinforcing relationships, screening for and treating CDs and related NCDs together rather than separately can more effectively reduce the suffering they cause. Hence, integrating interventions against CDs and NCDs can produce better clinical results than addressing them separately, and given the increasing overlap between the burdens of NCDs and CDs across the world, integration is now as crucial as ever.