The classic Shell Scenario methods book, 'Scenarios: An Explorer's Guide' (2003) is available for free download here.
The book is a graphics-heavy 'take' on scenario planning, quite whimsical, no doubt all about fighting the good fight with the Dutch engineers and Scottish accountants that 'are' the Shell establishment. It's hardly the last word in scenario methods, but still interesting for what it is.
On of the key things about it is it uses the metaphor of exploration and map-making to describe how to think about building scenarios. Says Shell: "Like a set of maps describing different aspects of a landscape, scenarios provide us with a range of perspectives on what might happen, helping us to navigate more successfully."
The book describes the approach used to develop Shell's ‘People and Connections’ scenarios circa 2000 under Ged Davis. As Shell comment: "Since then, scenarios guided by Albert Bressand have been published, and more recently Shell has published a summary of its Energy Scenarios, ‘Scramble’ and ‘Blueprints’, developed under the guidance of the current leadership. These have built on, and extended, our approach. Indeed, Shell has been working with scenarios for almost 40 years, and we are still learning."
Amen to that.