Context. Since the eighties, the combination of program analysis techniques has been increasingly recognized as a promising approach to overcome the limitations of standalone methods. While individual techniques, based on either static or dynamic analysis, address important challenges in software dependability, their integration often yields synergistic effects on precision, coverage and insights. Objective. This paper surveys a significant portion of the modern literature on combining program analysis techniques, consisting of 248 primary studies, with the aim of cataloging the types of interactions and synergies that were exploited to define combined-program-analysis techniques so far. The goal is to provide a structured understanding of why and how program analysis techniques can be conjoined, and which benefits can arise from their interactions. Method. We devise an original taxonomy that classifies combined-program-analysis techniques according to their aimed synergistic effects, inter-analysis workflows and interaction schemata (to which we refer to as mapping functions). We then map the primary studies to the taxonomy, answering research questions on which synergistic effects those studies pursued via the combination of analysis techniques, which inter-analysis workflows they embodied, and which types of mapping functions they exploited. Conclusion. Our taxonomy and literature mapping reveal the commonalities and the differences, in terms of goals and patterns, in the design of combined-program-analysis techniques. Thereby we provide a framework of concepts that can foster the ability of researchers and practitioners to reason on existing combined-program-analysis techniques, and steer further research on new useful combined-program-analysis techniques and analysis frameworks.