In this chapter, we shall provide some technical details regarding the most relevant processes/properties of a generic system, including the red thread that drives us in our research, namely the economic resilience under the crises overlapping. We shall proceed in the logical order of those processes/properties: (a) robustness; (b) resilience; (c) antifragility; (d) sustainability; (e) autopoieticity; (f) soundness. The analysis is conducted rather in a formalized way, in order to indicate as precisely as possible our positioning related to those crucial properties of the economic (larger, social) systems, processes and events. It is proposed a logical order (and, also, a chronological one) in which the six “defence lines” of an abstract economic/social system enter into action against perturbation, either internal or external, and effectively act to prevent, manage and (if possible—see the concept of antifragility) gain from those perturbations. The main focus is put on three items: rigorous definitions (based on sufficiency predicates), thresholds (that are crucial in the economic/social phenomenology, including, of course, the “red thread” of the book: the crisis) and the mechanisms involved in the evoked six concepts. In fact, the findings in this chapter will constitute the logical and methodological basis for all the next chapters of the book.