A new type of cascade laser, the so-called interband cascade laser based on type-II quantum well staircase structures, has been demonstrated recently. Here, we will discuss the design and modeling of the interband cascade lasers in connection with device performance. Normalized excess voltage and current will be introduced to evaluate how efficiently the input power is converted into the optical output power in the sense of the utilization of both injection current and applied voltage. Our modeling is based on Kane's eight-band k(DOT)p theory with envelope wave-function approximation and strain effects included. The calculated threshold current density, which includes contributions of radiative current, direct tunneling and Auger recombination, is significantly smaller than the experimentally observed value. This indicates that there are additional current leaking channels, which may be related to interface scattering and material defects, suggesting significant room for improvement. Our modeling also found that the device performance could vary substantially with temperature. Implications of our analyses and the modeling results will be interpreted in terms of carrier transport, optical gain and loss, as well as power efficiency.