Field emission is an alternative mechanism to classical thermionic emission for electron generation. It describes the phenomenon of electron tunneling from the surface of a material, typically metal, into vacuum under an electric field. This chapter focuses on the Carbon nanotube (CNT) X-ray technology and its potential applications in imaging and radiotherapy. CNT cathodes fabricated using the electrophoretic deposition method have shown stability at both high current and high current density. The CNT field emission technology has been investigated intensively in research institutions and industry, especially for field emission displays and X-ray generation. The chapter examines some of the systems under development/evaluation at the University of North Carolina at Chapel Hill. It discusses the specific designs and the properties of the CNT X-ray sources in these systems. Prototype stationary tomosynthesis systems using the CNT X-ray source array technology have been demonstrated for breast imaging.