Carbon nanotubes (CNTs) have emerged as some of the most promising materials for the technologies of the future. One of the most significant limitations to furthering the understanding and application of these fascinating systems is the lack of atomic-level structural control in their syntheses. Current synthetic methods produce mixtures of structures with varying physical properties. In this Letter, we describe the potential advantages, recent advances, and challenges that lie ahead for the bottom-up organic synthesis of homogeneous carbon nanotubes with well-defined structures. (C) 2010 Elsevier B.V. All rights reserved.