Bacterial communities form the backbone of virtually all known ecosystems, and play a fundamental role in nutrient cycling, primary production and consumption, or pollutant degradation. Bacteria form also the base of many food webs, and are subject to strong predation pressure by eukaryotes in aquatic and soil environments (Gasol et al., 2002; Rønn et al., 2002). Predation is a major cause of bacterial mortality (Pernthaler, 2005), and a driver of the genetic and functional structure of bacterial communities (Griffiths et al., 1999; Rønn et al., 2002; de Mesel et al., 2004; Bell et al., 2010). Predation also modulates the metabolic characteristics and the activity of bacterial communities, thereby contributing to nutrient cycling (Microbial loop, Clarholm, 1985; Bonkowski, 2004). Predation pressure is largely due to microfaunal predators (Ekelund and Ronn, 1994; Pernthaler, 2005), a functional group including protozoa and nematodes. A large fraction of all protozoan species are predators of bacteria, and free-living bacterivorous protozoa are present in all ecosystems ranging from sea to soil including deserts (Bouwman and Zwart, 1994; Ekelund and Ronn, 1994; Rodriguez-Zaragoza et al., 2005). Bacterivorous protozoa embrace many functional feeding groups, such as free swimming ciliates (one of the best known examples being the model organism Tetrahymena thermophila), heterotrophic flagellates, and amoebae. Each of these functional types has its own hunting characteristics and ecological niche (Coûteaux and Darbyshire, 1998). For example, naked amoebae dominate soil systems where they can access very small pores (Ekelund and Ronn, 1994), while in aquatic systems heterotrophic nanoflagellates are the main consumers of bacteria (Pernthaler, 2005). Nematodes, such as the well investigated Caenorhabditis elegans, are common in compost, soil as well as aquatic systems (Jensen, 1987; Neher, 2001), and form the second main group of bacterivorous organisms. Resisting predation improves survival in top-down controlled communities, and numerous bacteria from all phyla developed an array of defence mechanisms reducing predation pressure (Matz and Kjelleberg, 2005). During the last years, the investigation of bacterial defence strategies has been gaining in momentum. Technical advances, such as the availability of genome sequences and the solid investigation of pro- and eukaryotic model organisms, the better understanding of regulatory networks by bacteria and high-throughput analytics, allowed understanding a number of molecular mechanisms involved in bacterial defence. Additionally, the similarities between predator resistance and pathogenesis (Adiba et al., 2010) have fostered research on this subject by both environmental and medical microbiologists. The detection mechanisms involved in innate immunity and prey detection by free-living protozoa are very similar, and the datafrom immunological studies can help to better understand ecological processes (Stuart and Ezekowitz, 2008). Our understanding of how predator–prey interactions affect population dynamics and ecosystem stability has greatly improved during the last decades and provides a powerful interpretation framework to understand the causes and consequences of bacterial defence (Jeschke et al., 2002; Yoshida et al., 2003; Brose, 2008). Merging molecular tools with ecological models is a promising path of ecological research allowing to reliably predict the impact of different traits on the functioning and development of bacterial communities. This review aims at providing an interdisciplinary overview on these recent advances. First, I will present the known defence mechanisms involved in reducing predation pressure. Then, I will place these mechanisms in a more general ecological framework to discuss how distinct mechanisms affect predator–prey interactions. Finally, I will discuss direct and indirect consequences of bacterial defence on other ecological and evolutive processes. I will focus on interactions between bacteria and eukaryotic predators. Non-eukaryotic consumers, such as bacterial predators (e.g. Bdellovibrio) and viruses, also play a fundamental role in microbial ecology and evolution (see for example Weinbauer, 2004; Sockett, 2009), but for the sake of brevity and conciseness these will not be considered. Throughout this review, I will use the terms of ‘predators’ and ‘predation’ to describe the consumption of bacteria. Microbial ecologists often use grazing for what ecologists from other research fields would describe as predation, and both terms can be in the present context understood as synonyms.