Parasitoid insects are commonly compared with predators, because their development entails the host's death. However, there are strong indications that such departures from the usual habits of "true" parasites simply results from the similar size of the partners, which does not allow the host to survive loss of mass and energy inflicted by its developing parasitoid. Careful analysis of parasitoids' lifestyle rather suggests that thanks to their phylogenetic link with their hosts, they share many features which allow them to bring novel solutions to most ecological, behavioural and physiological constraints imposed by a parasitic lifestyle. Moreover, the exceptional behavioral capacities of insects. such as chemical communication, memory, capacity for learning or associative conditioning, makes parasitoids undisputable champions of host manipulation and regulation. Their ability to optimally manage their time, energy and host budgets, makes them lighly sophisticated and efficient parasites, despite their low reproductive potential. Special attention is paid here to the common association of parasitoids with prokaryotic cooperators or helpers, either bacteria or viruses. These take part in their physiology and behaviour, sometimes being necessary fortheir reproduction and successful exploitation of hosts, and display various degrees of integration. We present three recently documented examples. Many parasitoid Hymenoptera are infected (often multi-infected), with Wolbachia, endocytobiotic bacteria that seem to have been acquired from hosts through horizontal transfer. Wolbachia infection of haplo-diploid Hymenoptera can lead to various reproductive alterations, such as cytoplasmic incompatibility and thelytokous parthenogenesis, all of which result in strongly biased sex-ratios and affect the dynamics of host-parasitoid interactions. A special case is the braconid Asobara tabida, which has become totally dependent on a specific Wolbachia strain for egg production. How the insect lost its reproductive self-sufficiency in the course of evolution, how the bacteri re-establishes functional oogenesis, and to what extent the evolution of such obligatory mutualism is linked with the parasitic lifestyle, are especially puzzling and so far unanswered questions. Another parasitoid has proved to be occasionally infected with a non-pathogenic, vertically transmitted filamentous virus that induces infected females to oviposit into already parasitized hosts, contrary to uninfected females that regularly reject such hosts. Infection has been shown to be contagious through horizontal viral transmission among parasitoid larvae within the same host individual. Such contagious behaviour benefits the virus, which is now able to jump to uninfected insect lines and colonize populations. For the wasp, infection seems to vary from being advantageous to detrimental, depending on the abundance and availability of hosts. This recent discovery casts doubt on the current opinion that superparasitism acceptance is adaptive in parasitoids and has been selected for during the course of evolution. Virus-Like particles (VLP) are found in female Ichneumonidae and Baconidae. They are injected together with the egg into hosts, in which they depress or annihilate the cellular defense reaction. They also induce various alterations in host physiology that later benefit the parasitoid larva. Among various VLPs, PolyDNA viruses (PDV) has a true viral structure, with DNA circles and proteinic capsid. The viral genome is inserted into the host's nuclear genome and vertically transmitted in Mendelian fashion. It is intensively replicated in special cells of the female oviduct, then embedded within a capsid and released in large amounts into the lumen of the oviducts, before being injected into the new host. This "viral" genome is not self-replicative, and recent sequencing has shown that it shares more similarities with insect than with viral genes. Once injected into the host, some genes (of insect origin) express and synthesize peptides aimed at various targets, particularly host's haemocytes. Considering a variety of such VLPs (either with or without DNA) allows a discussion of the origin, acquisition and evolution of these particles. Clearly, such particles have become necessary for parasitization, and some of them can be considered as insect cell organites, whose function is to make possible the expression of some protective insect genes within the host itself, and at its own expense. none