The growing availability of nanotubes (NT) and the increased knowledge about their loading in polymers have prompted their incorporation in cementitious matrices. The main challenge towards achieving a significant enhancement in cement properties is an effective dispersion of the agglomerated NT. In my talk I will demonstrate how efficient NT (carbon or WS2) dispersion in cement results in substantial flexural and compressive strength enhancements at NT concentration below 0.15 wt%. The reinforcement by WS2 NTs remains significant after a variety of curing processes, suggesting a genuine nanoscale reinforcing effect. By employing a comprehensive fractography we show that the WS2 NTs inhibit crack propagation by bridging with a pullout failure mechanism.