The spread of invasive woody weeds in Africa, the challenges it presents for human livelihoods and nature, and the difficulty of effectively managing them constitute a complex social-ecological problem. This chapter outlines the specific issue of invasive Prosopis juliflora in eastern Africa, then describes the conception, structure, implementation and legacy of a multi-year, cross-disciplinary, interinstitutional, international project to address it. The Woody Weeds project, which ran from 2015 to 2021, involved four universities and eight institutes in Ethiopia, Kenya, Tanzania, South Africa and Switzerland. It spanned at least five scientific disciplines, trained graduate students and engaged stakeholders from local to national levels. The chapter summarizes the perceived successes of the project and the difficulties it faced in achieving its aims. It concludes with a section of lessons learned to inform the design of other projects to address the problem of invasive weeds or similar complex social-ecological problems.