Albert Einstein once claimed that "The measure of intelligence is the ability to change". Our successful survival in a permanently changing environment would not be possible without the ability to store and update new evidence, (re)-evaluate the choices and take adaptive decisions. This amazing ability to easily change according to the situation defines the cognitive flexibility of our minds. It is commonly held that the prefrontal cortex (PFC) is a critical hub for this ability. Despite the relevance of cognitive flexibility for day-to-day life, a mechanistic understanding of prefrontal coding of behavioral flexibility is still lacking. To fill this knowledge gap, the German Research Foundation (DFG) funds a new Research Unit FOR5159 "Resolving the prefrontal circuits of cognitive flexibility" with 4.1 million Euro for 4 years. FOR 5159 is a consortium headed by Prof. Ileana Hanganu-Opatz and Prof. Ilka Diester and integrates the universities Hamburg, Freiburg, Tübingen, Munich, Frankfurt, Mannheim, and Vienna and complementing local initiatives and strengthening the Neuroscience research at the national level. The FOR5159 aims to elucidate the mechanisms that enable neuronal populations in PFC to code for cognitive flexibility.