Among the bio-constraints affecting modern agriculture, weeds represent one of the major causes of crop losses, and their management is one of the most troublesome, expensive and labour-consuming agricultural practices. Effective weed management is a major challenge in modern agriculture, with a need to consider control efficacy, cost affordability, environmental safety, toxicity towards non-target organisms, and sustainability of the production system. Despite the progress in many technological fields, most of the weed management practices are still based on the use of synthetic chemicals. In the developed world, the amount of herbicides used is significantly higher than that of insecticides or fungicides. Despite the dependency of agriculture on herbicides, two trends are jeopardizing their use. A large number of herbicides have already been withdrawn for regulatory reasons because of toxicology (both human and environmental) issues. Furthermore, they are becoming less effective as the result of rapid evolution of herbicide resistance of weeds. These issues have renewed the interest in the development of biological alternatives to synthetic herbicides. However, despite decades of effort and the discovery of many interesting microbial agents, their use is still very limited, replacing or augmenting only a small part of the chemical market with minor integration with conventional control methods. The lack of efficacy is due to biological (insufficient virulence, lack of stability, defense mechanisms of the targets, interaction with other microorganisms, and narrow microenvironmental requirements); technological (difficulties in fermentation and formulation, short shelf life); environmental (interaction with water, soil characteristics, sensitivity to physical and chemical factors) and commercial (high costs of production and registration in relation to market size) constraints. Novel biotechnologies provide new opportunities for enhancing biocontrol microorganisms by allowing a better knowledge of their characteristics and improvements in their properties. These biotechnologies are not widely applied in weed biological control, compared to other agricultural biocontrol (biofungicides, bioinsecticides) applications.