The effective charge of colloidal particles and polymers, produced by weak acid or weak base functional groups, experiences variation with environmental pH due to the ionization of these groups. The pH = -log 10 (a H ), is defined as the negative decadic logarithm of dimensionless proton activity, a H = c H e βµ ex H /c , where c = 1 M is the standard concentration, β = 1/k B T , and µ ex H denotes the excess electrochemical potential. The stability of colloidal particles in aqueous suspensions is intrinsically connected with their surface charge density, which is controlled by the pH of solution. Similarly, the activity of many biologically relevant proteins and polyelectrolytes is influenced by the solution's pH and ionic strength. Quantitative understanding of charge regulation in such complex systems is, therefore, crucial for a wide range of industrial and medical applications.