The document describes a method called MusRank for ranking species in mutualistic networks based on their importance and vulnerability. Mutualistic networks involve mutually beneficial interactions between plants and animals, and play a key role in biodiversity. MusRank ranks species based on both their importance, determined by the number and vulnerability of their partners, and their own vulnerability, bounded by their least important partner. The ranking is robust and outperforms other methods. MusRank can help identify key species to focus on for conservation in these important ecosystems.