This document discusses isoelectric focusing (IEF), a technique that separates molecules like proteins based on differences in their isoelectric point (pI). IEF works by placing proteins in an immobilized pH gradient gel and applying an electric field, which causes the proteins to migrate until they reach the pH that matches their pI and become neutrally charged. Common applications of IEF include separating, characterizing, and purifying proteins and peptides, as well as its use in forensic analysis, taxonomy research, and genetic marker typing.