This book constitutes the thoroughly refereed post-conference proceedings of the 26th International Workshop on Algebraic Development Techniques, WADT 2022, held in Aveiro, Portugal, in June 2022. The 6 revised papers presented together with 2 invited papers were carefully reviewed and selected from 25 submissions. The contributed presentations covered a range of topics about the algebraic approach to system specification, which encompasses many aspects of the formal design of software systems. Originally born as formal method for reasoning about abstract data types, the algebraic approach now covers new specification frameworks and programming paradigms (such as object-oriented, aspect-oriented, agent-oriented, logic, and higher-order functional programming) as well as a wide range of application areas (including information systems, concurrent, distributed, and mobile systems).