Summary: The theory presented in the paper consists of two parts. The first is devoted to basic concepts and principles such as the very concept of a subdifferential, trustworthiness and its characterizations, geometric consistence, fuzzy principles and calculus rules, methods of creation of new subdifferentials etc. In the second part we study certain specific subdifferentials, namely, subdifferentials associated with bornologies, their limiting versions and metric modifications. For each subdifferential we verify that the basic properties discussed in the first part are satisfied and prove calculus rules for two main operations: summation and partial minimization. Separate sections are devoted to the Fréchet and limiting Fréchet subdifferentials and to the approximate \(G\)-subdifferential. For the last two new definitions are given which lead to a certain unification and simplification of analysis. The sum rule for these two subdifferentials is proved with the so-called ``linear metric qualification condition'', so far the most general. In the last section we briefly discuss how other operations reduce to the two mentioned basic operations and give the corresponding calculus rules (with suitable versions of the metric qualification conditions).