This paper proposes a generalized approach combining two-way ranging (TWR) and passive ranging methods, called active-passive two-way ranging (AP-TWR). The proposed approach offers a generalized solution for a wide range of anchor configurations in positioning systems. The possibility to define active-passive and passive-only anchor roles allows scaling the system to improve the root-mean-square-error (RMSE) of the ranging estimations and the air time occupancy. Practical experiments show that with the proposed method consisting of 5 active-passive anchors and a single passive anchor, the RMSE is improved by 7.4% and the air time occupancy by 12.5% as compared to the single-sided TWR method with a 6 anchor configuration. Moreover, simulation results show that a maximum theoretical RMSE improvement of 31.7% can be achieved with the proposed setup.