Two ruthenium compounds, namely [ImH]trans-[RuCl4(Im)(dmso-S)] (NAMI-A, Im = imidazole) and [IndH] trans-[RuCl4(Ind)2] (KP1019, Ind = indazole) have already completed phase I clinical trials as anticancer agents. They both have properties different from platinum anticancer drugs: for example, NAMI-A is selectively active against metastases of solid tumors. They show that in the field of anticancer metal drugs a new approach, based on targeted therapies, is possible. After a concise history of ruthenium anticancer compounds, this contribution will focus on ruthenium-dmso complexes and, in particular, on NAMI-A. Particular emphasis is given on the challenges that are inherent to this field: how to develop new anticancer ruthenium compounds and how to select new active compounds that manifest their anticancer activity through non-conventional mechanisms.