This dissertation provides the first systematic analysis of the dynamic energy efficiency of vertical-cavity surface-emitting lasers (VCSELs) for optical interconnects, a key technology to address the pressing ecological and economic issues of the exponentially growing energy consumption in data centers. Energy-efficient data communication is one of the most important �elds in “Green Photonics� enabling higher bit rates at signi�cantly reduced energy consumption per bit. In this thesis the static and dynamic properties of GaAs-based oxide-confined VCSELs emitting at 850 nm and 980 nm are analyzed and general rules for achieving energy-efficient data transmission using VCSELs at any wavelength are derived. These rules are verified in data transmission experiments leading to record energy-efficient data transmission across a wide range of multimode optical fiber distances and at high temperatures up to 85°C. Important trade-offs between energy efficiency, temperature stability, modulation bandwidth, low current-density operation and other VCSEL properties are revealed and discussed.