IBM Design Thinking Field Guide
This toolbox contains 11 tools and 20 pages of design thinking theory and principles. The button link takes you directly to a PDF download.
It is an internal document, aimed at helping people to run IBM Design Thinking activities with teams. The theory pages at the beginning take you through key principles including 'The Loop', a wheel of 'Six universal experiences' used to frame a user experience design project, and the overlaps between IBM Design Thinking and Agile.
It was developed by Seth Johnson at IBM and is regularly updated.