This document provides an overview of microbial biofilms. It discusses how biofilms form and develop through attraction, adhesion, aggregation and accumulation of cells and extracellular matrix. The architecture and properties of biofilms are described as depending on nutrient levels and forming complex structures with channels. Biofilms provide benefits for microbes like cooperation, gene transfer and protection. They display higher resistance to toxic substances than planktonic microbes. The document traces the history of biofilm research and argues microbiology was previously misled by a focus on planktonic cultures rather than natural biofilm growth.