Bacteria make an either-or-decision in their natural environment whether they inhabit a human or other microbial niches. They either form sessile and multicellular communities known as biofilms. Or, they exist as single cells in a motile and planktonic state. The decision by bacteria to do one or the other, which is crucial for their survival, can profoundly impact our lives. Bacterial biofilms form on many surfaces, from the hull of an aircraft carrier and the surface of a pipeline to a medical implant and a contact lens. Bacterial pathogens tend to cause acute infections in their motile or planktonic state whereas their biofilms often result in chronic and recurrent infections. Bacteria form biofilms by producing biofilm matrix materials which organize and protect the bacteria within. Their motile and planktonic state frequently requires the construction and the functioning of a bacterial motility apparatus such as a bacterial flagellum or type IV pilus (T4P). The Yang lab focuses on how bacteria make and execute these critical lifestyle decisions.