With a field so broad in both breadth and depth as that making up the contemporary study of complex systems, it is well nigh impossible to cover all the bases underlying the development of well argued, robust and relevant understanding of these systems. That is one of the reasons why the international journal Emergence: Complexity and Organization has offered a Classical Paper in each issue. Now, in this current volume we have made available in one publication venue the diverse Classical Papers that have been published so far in E:CO. These papers are offered not only to enrich our current understandings by exhibiting the historical background to many of today’s leading complexity-based ideas, perspectives, and methods. They are also gathered here to help address some of the difficulties confronting not only complexity thinkers, but for that matter any thinker sincerely trying to grasp the novel situations and novel difficulties we face in modern times.