The USRP X300 is a high-performance, scalable software defined radio (SDR) platform for designing and deploying next-generation wireless communications systems. The hardware architecture combines two extended-bandwidth daughterboard slots covering a daughterboard-dependent frequency range with up to 160 MHz of baseband bandwidth, multiple high-speed interface options (PCIe, dual 10 GigE, dual 1 GigE), and a user-programmable Kintex-7 FPGA in a convenient desktop or rack-mountable half-wide 1U form factor. In addition to providing best-in-class hardware performance, the open-source software architecture of the USRP X300 provides cross-platform UHD driver support, making it compatible with a large number of supported development frameworks, reference architectures, and open source projects.