It is not possible to examine a situation or system of interest in its entirety or from all possible perspectives. Boundaries inevitably determine what is included and excluded, which can have practical, political, and ethical consequences. Critical systems heuristics (CSH) offers a framework of questions posed in descriptive (what is) and normative (what should be) modes that can inform boundary setting and resetting in any inquiry, intervention, or evaluation. This chapter first introduces CSH and its early developments and influences. The next section highlights recent examples on the use of CSH from Colombia and New Zealand. The subsequent section identifies several open questions regarding CSH and its applicability. The chapter concludes with reflections on future directions.