Biological pest control in greenhouse crops is usually based on periodical releases of mass-produced natural enemies, and this method has been successfully applied for decades. However, in some cases there are shortcomings in pest control efficacy, which often can be attributed to the poor establishment of natural enemies. Their establishment and conservation of population natural enemies can be enhanced by providing additional resources, such as alternative food, preys, hosts, nectar, pollen, plant sap, oviposition sites and shelters. Natural enemies respond to odors that are produced by their prey/host species, such as sex pheromones or alarm pheromones. Therefore, their efficacy can be enhanced by using volatiles. Moreover, Natural enemies just like plants, can be impacted directly by greenhouse climate parameters, such as, temperature, vapor pressure deficit, light intensity and quality, and day length. The side-effects on conservation of natural enemies can be achieved by selecting pesticides that are compatible or as close to compatible as possible with natural enemies. The Methods that support the establishment of natural enemies are often associated with increased complexity within food webs of natural enemies, prey and food sources, therefore the minimizing disrupting food web complexities. On the other hand, a proper greenhouse management system would lead to successful pest control in covered crops. This approach not only guaranty high quality and quantity greenhouse products, but also prepare a safe and chemical free environment for farmers and their natural enemies. In this article, we review some of the tools and methods mentioned in the protection and the establishment of natural enemies in the greenhouse, weaknesses will be identified and some of them are optimized for some studies conducted recommended.