This document provides an overview of receptor pharmacology and classification. It discusses the main types of receptors, including ligand-gated ion channels, G protein-coupled receptors, kinase-linked receptors, and nuclear receptors. Ligand-gated ion channels open or close in response to ligand binding, allowing ions to pass through. G protein-coupled receptors have 7 transmembrane domains and signal through G proteins and second messengers. Kinase-linked receptors activate intracellular kinases. Nuclear receptors form dimers and translocate to the nucleus to regulate gene transcription. Receptors play a key role in cellular signaling and are important drug targets.