In a fermentation process, micro-organisms generally are held in a fermentation substrate under certain environmental conditions to introduce desired changes in the substrate. The objective can be the production of microbial cells, the production of enzymes or metabolites, or the process can have the aim to transform one specific component into another. There are ample and worldwide examples of fermentation processes in the food and in other industries. Also for the insect industry, fermentation technology can provide a number of opportunities. This presentation will focus in the first place on fermentation of rearing substrates for insects and in the second place on fermentation of the harvested insects. Substrates can be fermented, either as a liquid state fermentation or as a solid state fermentation or silage process to improve the shelf life of the substrates, in particular when the supply of substrate to the rearing facility is higher that the feeding rate, and to increase the digestibility and microbial safety of the substrates. While examples of this practice can be found in industry, e.g. the fermentation of food waste or potato peels, the impact of fermentation of the substrate on insect growth is hardly documented in literature. More public data with respect to the impact of e.g. the pH reduction by fermentation and the altered (micro)structure of the substrate on insect growth and microbiology are needed for the sector. Within our research group Lab4Food, we currently study the fermentation of substrates for rearing of black soldier fly larvae (BSFL) by lactic acid bacteria (LAB) isolated from the BSFL gut. Possibly, one or more isolates could first serve as starter culture to ferment the substrate for preservation and digestibility improvement, and then later, when the starter has colonized the substrate, it can behave as a probiotic during rearing and enhance larval growth. In addition to being useful for rearing substrates, fermentation potentially brings added value to harvested insects. Similar as to shrimp paste, it is possible to pulverize insects, add a starter culture and ferment the paste. Literature on this practice is extremely scarce, but research at Lab4Food pointed out that blanched mealworms cannot be fermented with commercial meat starter cultures as a whole, but it is possible after fragmentation into paste, as indicated by the rapid pH decrease. Fermentation of mealworm paste decreased protein content and solubility (as they were consumed by the starters), but it increased shelf life of the paste in contrast to the use of traditional meat preservatives. Experience with BSFL fermentation using the same protocols as for mealworms is currently being built up and will be discussed.