Multipath TCP is a new transport protocol that enables systems to exploit available paths through multiple network interfaces. MPTCP is particularly useful for mobile devices, which frequently have multiple wireless interfaces. However, these devices have limited power capacity and thus judicious use of these interfaces is required. In this work, we develop a model for MPTCP energy consumption derived from experimental measurements using MPTCP on a mobile device with both cellular and WiFi interfaces. Using our MPTCP energy model, we identify the operating region where MPTCP can be more power efficient than either standard TCP or MPTCP. Based on our findings, we also design and implement an improved energy-efficient MPTCP that reduces power consumption by up to 8% in our experiments, while preserving the availability and robustness benefits of MPTCP. © 2014 ACM.