This paper analyzes the dynamics of diffuse charge in electrochemical systems, focusing on the response of a symmetric binary electrolyte between parallel-plate, blocking electrodes to a suddenly applied voltage. The study begins with a historical review of electrochemistry, colloidal science, and microfluidics, highlighting the importance of diffuse charge dynamics in various applications. The model problem involves a dilute z:z electrolyte between parallel-plate electrodes separated by 2L, with compact Stern layers on the electrodes. The Nernst-Planck-Poisson equations are linearized and solved using Laplace transforms for small voltages, while numerical solutions are obtained for large voltages. The "weakly nonlinear" limit of thin double layers is analyzed using matched asymptotic expansions, revealing multiple time scales and the role of neutral-salt adsorption. In the "strongly nonlinear" regime, bulk concentration gradients and transient space charge are observed. The paper concludes with an overview of more general situations involving surface conduction, multi-component electrolytes, and Faradaic processes. Key findings include the primary time scale for diffuse-charge dynamics, τc = λD L / D, and the importance of nonlinear effects in charge relaxation. The study also discusses the limitations of classical circuit models and the need for more sophisticated mathematical analyses in electrochemical systems.This paper analyzes the dynamics of diffuse charge in electrochemical systems, focusing on the response of a symmetric binary electrolyte between parallel-plate, blocking electrodes to a suddenly applied voltage. The study begins with a historical review of electrochemistry, colloidal science, and microfluidics, highlighting the importance of diffuse charge dynamics in various applications. The model problem involves a dilute z:z electrolyte between parallel-plate electrodes separated by 2L, with compact Stern layers on the electrodes. The Nernst-Planck-Poisson equations are linearized and solved using Laplace transforms for small voltages, while numerical solutions are obtained for large voltages. The "weakly nonlinear" limit of thin double layers is analyzed using matched asymptotic expansions, revealing multiple time scales and the role of neutral-salt adsorption. In the "strongly nonlinear" regime, bulk concentration gradients and transient space charge are observed. The paper concludes with an overview of more general situations involving surface conduction, multi-component electrolytes, and Faradaic processes. Key findings include the primary time scale for diffuse-charge dynamics, τc = λD L / D, and the importance of nonlinear effects in charge relaxation. The study also discusses the limitations of classical circuit models and the need for more sophisticated mathematical analyses in electrochemical systems.