Multipath TCP (MPTCP) allows multi-homed hosts to make use of multiple addresses over a single TCP connection. This talk will cover the software architecture of a FreeBSD implementation of MPTCP, as well as presenting some case studies and performance results. Multipath TCP (MPTCP) was designed as an extension to TCP, allowing a multi-homed host to utilise multiple network interfaces when transferring data. MPTCP is in the process of being standardised by the IETF as RFC 6824. Supported by funding from Cisco Systems, the Centre for Advanced Internet Architectures released several patches against FreeBSD-10 (from March 2013) to add rudimentary MPTCP capabilities and code paths. More recently, the FreeBSD Foundation provided funding to continue development of the MPTCP stack, building on the existing work. The stack has since then been re-designed and improved beyond the early experimental versions. In this talk I will provide an overview of the Multipath TCP (MPTCP) protocol before discussing the software design, features and performance of our FreeBSD MPTCP implementation. I will also present some basic performance testing, case studies and usage examples (showing how MPTCP reacts to different paths coming and going while connections stay active).