Abstract: This paper argues that a central explanatory role for the concept of Umwelt in theoretical biology is to be found in developmental biology, in particular in the effort to understand development as a goal-directed and adaptive process that is controlled by the organism itself. I will reach this conclusion in two (interrelated) ways. The first is purely theoretical and relates to the current scenario in the philosophy of biology. Challenging neo-Darwinism requires a new understanding of the various components involved (...) in natural selection processes. An important prerequisite for the explanation is the ability to understand development in a teleological way. Here, the concept of Umwelt plays a crucial role: if organisms are responsible for generating adaptive variation in specific environments, we need a theory that explains the context-dependent nature of adaptively oriented processes. The Umwelt is thus a central element in determining the goal that an adaptive process pursues. The second path in my analysis also has a historical dimension. I will present Karl Ernst von Baer’s reflections on teleological development and his influence on von Uexküll's thinking. I will present various ideas developed by von Baer, such as the distinction between Ziel and Zweck and the use of musical metaphors, which can help to understand development teleologically and give von Uexküll’s theory a central place in this framework. (shrink)