Sustainable Tourism as a paradigm of development originated from the convergence of several streams of thought nearly three decades ago. It has tended to follow a ‘smaller is better’ theme but there are significant questions about the saliency of this theme in a 21st world characterized by change, contentiousness, conflict and uncertainty. Sustainable tourism is often linked with ecotourism and a dependency on natural environments as a principal resource providing the basis for an experiential product. The rise of systems thinking has led to new, and potentially more useful insights, about tourism as an economic development strategy in this context. Questions about the future ability of sustainable tourism to spur not only progress but the advancement of knowledge are presented and debated in this probe. The probe begins with a presentation by Steve McCool who presents a brief history of the development of the concept of sustainable tourism, provides an overview of how 21st century conditions are significantly different than those in which the term arose and suggests a reformulation of the concept to one of enhancing resiliency in the face of stresses and strains on communities. Responses by David Weaver, Richard Butler, Ralf Buckley and Brian Wheeller suggest that academia has a poor record of performance in addressing the real life issues confronting the globe's economic woes through sustainable tourism. Several feel that global economic and political power are so overwhelming as to make debates on sustainable tourism irrelevant. McCool responds to these criticisms by suggesting that knowledge is the principal barrier to progress.