This is an individual chapter of Theory of Constraints Handbook. This chapter provides an introduction of the Thinking Processes, their nature and use; addressing the TP's conceptual, philosophical and methodological foundations; cataloguing their use and practice as reported in the published literature; discussing the need, the design and purpose of the TP's; and reviewing their efficiency, by themselves, in concert with one another, or with other decision-making techniques. We discover that TOC acts as a near-complete methodological set on its own, and note synergies through multi-methodological use. We determine and talk about concerns raised in the literature: the need to developed further acknowledgment from expert groups and academic community, and gaps such as longitudinal and empirical studies. We suggest forging links with cognate fields and disciplines to build further acceptance for TOC.