Pseudomonas syringae is a bacterial plant pathogen that can lead to heavy losses in crop production. This bacteria is a very good model to study the infection processes, as it can cause disease in Arabidopsis thaliana, a well-studied plant model. This text presents an overview of the bacterial pathogenesis from a molecular biology perspective, and explains the role of plant responses in stopping the spread of the infection. Plant hormones are important elements for plant defence. Their role and how the pathogen interferes with their action will be discussed further.