Cooperation is ubiquitous in the natural world. Genes have come together in genomes, cells work together in multicellular organisms, animals cooperate in societies, different species can engage in interspecific mutualisms and humans cooperate with each other in a myriad number of ways. Yet, cooperation represents a major evolutionary challenge, since uncooperative, selfish individuals would often be expected to be at an advantage relative to more cooperative group members. In my research I study how this "free-riders" problem can be solved and what mechanisms can help to maintain stable and robust cooperative behaviour. Hereby, I use social insects (ants, bees and wasps) as the major model systems. My work has led to various original insights and discoveries, e.g. that cooperation in insect societies is to a large extent socially enforced and that some conflicts in insect societies resemble tragedies of the commons , which previously were known mainly from human systems. Recently, I also extended my research into the area of sociogenomics, to get a grip on what genes are involved in social behaviour, and I have also started to work with other model systems, including humans, microorganisms and swarms of robots. My research makes use of a range of cutting-edge techniques including theoretical modelling (game theory, population genetic and inclusive fitness models, agent-based models), video-assisted behavioural observation, chemical ecology (gas chromatography) and genetic, genomic and proteomic analyses.