 1. In situations where there is strong density stratification, hydromagnetic turbulence exhibits new characteristics, the creation of magnetic flux concentrations. 2. We provide a theoretical review of this mechanism, which is now known as the negative effective magnetic pressure instability. 3. Additionally, we present direct numerical simulations of force turbulence in strongly stratified layers, and compare them with corresponding mean field simulations. 4. Finally, we discuss the similarities between these findings and their relevance to sunspot formation. This article was authored by Axel Brandenburg, Igor Rogachevsky, and Nathan Cleoran.