Grafting solid surfaces with charged polyelectrolyte (PE) brushes ensures effective functionalization of such surfaces enabling these surfaces to be used in a myriad of applications such as fabricating surfaces with desired wettability and protein adsorbability, making nanochannels capable of enhanced current rectification, sensing ions and biomolecules, and generating nanoscale electrokinetic energy, and designing nanoparticles for drug delivery, oil recovery, and water harvesting. All these applications rely on the ability of these functionalized surfaces to strongly respond to changes in environmental stimuli, such as the pH and the salt content of the solution in which the brushes are present, temperature and humidity of the surroundings, etc. Also, capturing the equilibrium behavior of these brushes (in response to these stimuli) using different theoretical, computational (both coarse-grained simulations and all-atom molecular dynamics simulations ), and experimental methods has been essential to optimize these applications and unravel novel facets of equilibrated PE brush behaviors.