Nematodes are unsegmented roundworms that numerously and successfully adapted to all regions and environments on earth. The last ones were usually classified into feeding types: free-living, predaceous, and parasitic ? including plant-parasitic. They are of great significance in terms of damage they cause. Plant-parasitic nematodes have been reported to be responsible for the losses amounting to over $100 billion throughout the world. Because of the big difficulties in their eradication some of them are considered as quarantine species. The plant-parasitic nematodes are controlled using chemical methods ? mainly chemical nematicides. However, because of many drawbacks including health and environmental concerns, other control methods are considered. One of them is biological control and application of antagonistic microorganisms to decrease densities of nematodes populations. Microbial antagonists parasitizing various developmental stages of their hosts may affect nematodes by secretion of antibiotics, toxins and other secondary metabolites. The most important virulence factors are extracellular enzymes that participate in destroying the nematodes' cuticle or the egg-shell or in further phases of infection. This publication presents the examples of microorganisms investigated in terms of biological control, those that are already available commercially as well as some mechanisms involved in nematode-microbes interactions.