<p>Carbon nanotubes have attracted extensive interest owing to their extraordinary properties and wide applications in many fields. Among various types of carbon nanotubes, only ultralong carbon nanotubes with macroscale lengths, low defect concentrations, and high degrees of alignment can fully demonstrate their intrinsic performance. These attributes make ultralong carbon nanotubes highly promising for applications in cutting-edge fields, such as carbon-based integrated circuits, ultra-strong fibers, and transparent conductive films. However, the mass production of ultralong carbon nanotubes with precise structural control remains a major challenge, limiting their widespread applications. In the past decades, great progress has been achieved in the study of ultralong carbon nanotubes. In this review, we summarized the growth mechanisms and the controlled synthesis strategies of ultralong carbon nanotubes. Then, we introduced the advanced applications of ultralong carbon nanotubes in many areas, such as field-effect transistors, sensors, and photodetectors. Finally, we discussed the remaining challenges and offered our perspectives on the future directions of this field.</p>