Information theory was formulated by Shannon as the theory of communication. However, it has become a popular tool for answering a related — but a different — set of questions: namely, which features of a system are essential for its description, and therefore, must be preserved in a model describing it? These tools were developed largely in the context of biophysical systems, where traditional theoretical physics toolbox is insufficient to identify the relevant terms. I will walk us through a series of examples in different experimental biological and synthetic systems, where information theory has been used in this way.