Biofilm formation plays an important role in antimicrobial resistance, posing a global threat to the economy and public health. Hence, discovery of novel antagonists is critical. In this chapter, we introduce a class of compounds, brominated furanones, which have a broad spectrum of activities against bacterial multicellular behaviors, such as biofilm formation and quorum sensing. The application of these compounds and the mechanisms of inhibition are reviewed. This chapter also reviews inhibitors of quorum sensing in Gram-positive bacteria, especially those of staphylococci. The use of these inhibitors to prevent and treat biofilm diseases in humans and animals is shown in subsequent chapters.