Some plant-parasitic nematodes need to spend a significant part of their life cycles within plants while others have long-lasting biotrophic interactions with their hosts. In each case, these nematodes will need to suppress host defences. Large numbers of candidate effectors - proteins that nematodes introduce into their hosts - have been identified from a variety of nematode species as a result of genome and transcriptome projects. There is now a focus on functional characterization of these proteins. This has led to the identification of nematode proteins that suppress different types of host defence responses. Here we review progress towards understanding how nematodes manipulate host defences and how hormone signalling related to defence responses is targeted by nematodes.