Two-dimensional (2D) electrode materials present opportunities to enhance the efficiencies of electrochemical processes involved in electrocatalytic reactors, batteries, and supercapacitors. In this review, we discuss the theoretical basis of classical and quantum confinement effects, including how they modulate the performance of 2D electrode materials, in the light of recent experimental advances in the area. In particular, we discuss ion transport in the interstitial channels of 2D layers with and without spacers, the mechanisms and the underlying theories of mass and electron transport, and the effect of step edges, defects, and dopants on the mechanism and kinetics of electron transport in 2D electrode materials. We identify several opportunities for future work involving first-principles calculations, molecular dynamics simulations, as well as the development of analytical theories. Overall, this article not only provides a brief theoretical overview of electrochemical phenomena in 2D electrode materials, but also details several knowledge gaps in the field. ● Electrochemical phenomena in 2D electrode materials are discussed in the context of electrocatalytic reactors, batteries, and supercapacitors. ● Role of nanoconfinement in modulating the transport of molecules/ions and the structure/dynamics of electrical double layers is reviewed. ● Application and accuracy of various theories to model electron transfer in 2D electrode materials is discussed. ● Modulation of electrochemical activity of 2D materials due to edges, defects, and dopants is highlighted. ● Various knowledge gaps are outlined and the presented theoretical insights are contextualized with recent experimental results.