Clarity of definitions is fundamental to the successful completion of any interdisciplinary project. In this chapter, we focus on defining a number of key terms that recur throughout the volume, and thus it acts as both a foundation and glossary for understanding the material covered. Ideas of resilience, self-organization and complexity are widely used across in constituent disciplines discussed in Chap. 1, but their use varies and we attempt to define this variation and thus the context of use in the book. There is also a strong emphasis on pattern, so we provide here an initial definition, to be followed up in more detail in Chaps. 7 and 8. We then move onto the specific nature of drylands and the need to understand land degradation within them and through them. How the mode of study affects our understanding is the next theme, in particular how case studies based in different places can be generalized, given the variations in landscape and vegetation type within them. Following an initial summary of the preceding material to evaluate why self-organization and complexity are useful frameworks for understanding patterns and processes in drylands, the chapter concludes with an overview of the deterministic and stochastic frameworks for understanding pattern