This chapter provides an overview of the cost of energy and scenario planning. These broad, often overlapping themes, underpin wider aspects of energy security and energy planning. In exploring the cost of energy and scenario planning, complexities arise including aspects related to the modern day issue of climate change and drive for sustainability. For management decisions to effectively address the multi-faceted nature of an increasingly globalized economy, national and international energy markets must harness approaches that adopt multi-perspective and holistic planning. Ultimately, addressing the energy conundrum is a 21st century challenge. This challenge is associated specifically with the urgent need to decarbonize economies without compromising economic development, all the while striving towards energy and environmental security. This means that revisiting the question of cost is an imperative for all stakeholders. ‘What is the cost of energy?’ is as pertinent a question as ever. In this chapter we will examine and explain why several answers are misleading and unsatisfactory.