Reduction in herbicide use will trigger changes in weed communities. Improving our capacity to identify farming management options that will lead to weed communities offering interesting trade-offs of functions is thus timely. Functional approaches are offering a robust framework to quantify and understand the underlying mechanisms that link farming management to weed functions. This chapter reviews recent advances in our understanding of the role of weed diversity, of key weed functional traits and of their intraspecific variability in the functioning of the agroecosystem. It presents recent progress in the emerging field of weed multifunctionality assessment. While the scarce data available supports that some weed communities can deliver several beneficial functions without causing much crop yield loss, the challenge for the future will be to demonstrate that there are interesting weed functions trade-offs that can be achieved over a wide range of agronomic and weeds contexts, that are cost-effective and credible for farmers to adopt.