This chapter deals with the application of Vertical-Cavity Surface-Emitting Lasers (VCSELs) as directly-modulated light-sources in optical interconnects. It shows that VCSEL-based optical interconnects are going to replace the conventional copper-based technology. VCSELs can deliver higher bandwidths below the cost of copper and enable highly scalable solutions with their small footprint. If lasers have to provide excellent beam quality at low cost and energy-consumption, VCSELs are the current technology of choice. Directly modulated VCSELs have bandwidth limitations that must be conquered to enable the highest bandwidths at ultra-low cost. The High-Speed, Temperature-Stable 980-nm VCSELs made at the Center of Nanophotonics at the Technical University of Berlin were processed in a coplanar low-parasitic ground-signal-ground contact pad layout incorporating thick BCB passivation layers. VCSELs designed to work at ultra-high bit rates don’t automatically get more energy efficient just by simply reducing the pumping current and the bit rate.