The mechanism of field emission from a metal surface was well explained based on the quantum mechanics in early 20th century. Since then, various materials have been studied for field emitters. However, so far, we have been using only limited materials as a field emitter and an application in some area requires further scientific understandings and technological advancements. In this paper, we review the current status of researches in field emission and emission phenomena of carbon nanotubes (CNTs). This may include current saturation induced by gas adsorbates, screening effects, high current emission, degradation of emitter, and field enhancement factor. We also introduce the present status in the development of various CNT-based field emission devices and discuss their performances. In this part, various potential applications such as field emission display, ionization gauge, X-ray gun, and lamp will be presented.