Pollination is an essential process for the sexual reproduction of seed plants, and the majority of flowering plants worldwide benefit from insect pollinators. However, insect pollinators have been declining globally, and their decreasing numbers and species diversity could have serious environmental, food production, and economic consequences. Several factors have been proposed to explain pollinator decline, including land-use changes, biodiversity loss, climate change, and pesticide use. In this dissertation, I investigated the impacts of glyphosate, the world’s most widely used herbicide, and its commercial formulations (glyphosate-based herbicides) on the buff-tailed bumblebee (Bombus terrestris). Although concerns have arisen in recent decades about glyphosate being more harmful than previously thought, there is no consensus on the extent of its effects, specific mechanisms, or exposure routes. First, I investigated whether bumblebees could be exposed to glyphosate while visiting flowers. The results showed that bumblebees did not avoid glyphosate-sprayed plants, even when untreated plants were available. Second, I studied the effects of glyphosate on cognitive abilities considered crucial for bumblebee survival. Glyphosate-based commercial formulations did not affect the duration of daily foraging trips in freely flying bumblebees, but the number of trips nearly doubled, while the number of flower visits per trip decreased. Exposure to the commercial formulation did not impair the bees' ability to return to the colony. While the formulation had no impact on learning or memory, the same amount of pure glyphosate weakened learning performance. Third, I examined the effects of glyphosate and its commercial formulation on the gut microbiota of bumblebees, as some gut bacteria are potentially sensitive to glyphosate. The results indicated that pure glyphosate increased microbiota diversity, whereas the commercial formulation decreased it. However, both treatments reduced the abundance of Snodgrassella alvi, a bacterium beneficial to bumblebee immunity. Overall, my findings suggest that both glyphosate and its commercial formulations have harmful effects on bumblebees. My research provides new insights into exposure routes and individual-level effects, but further studies are needed, particularly on glyphosate’s mechanisms and its impact on entire colonies.