Vegetables are an irreplaceable part of human diet as they bestow human body with vitamins, proteins, vital micro- and macronutrients, etc. They are constantly encountered with various phytopathogens like bacteria, fungi, viruses, nematodes and herbivores and environmental stressors like temperature, drought and salinity that have an adverse impact on their quality and yield. To escalate the growth and production and to counteract various stressors, chemical fertilizers and pesticides are indiscriminately used by vegetable growers. Their extensive use causes various threats to the environment, humans and other living organisms. Considering the harmful effects of these synthetic pesticides and chemical fertilizers, it has become necessary to cut down their use and shift to biological crop improvement methods for the enhancing the quality and quantity of vegetable crops. Microorganisms like arbuscular mycorrhizal fungi, plant growth promoting bacteria and various entomopathogenic nematodes act against different types of stresses and provide environment friendly and sustainable alternative for raising the productivity and improving the quality of vegetables. Thus, this book chapter highlights the role of various microorganisms against biotic and abiotic stresses faced by vegetables and different mechanisms employed by them in quantity and quality improvement in vegetable crops.