Matthew Walker opens Why We Sleep with an urgent, evidence-heavy premise: sleep is not a passive, dispensable luxury but an active biological necessity underlying nearly every dimension of physical and mental health, and modern society's chronic sleep deprivation represents a significant, underappreciated public health crisis.

Walker's foundational argument:

• He presents sleep as performing dozens of distinct, essential biological functions simultaneously — memory consolidation, immune support, emotional regulation, metabolic maintenance — meaning inadequate sleep doesn't simply produce tiredness but measurably degrades functioning across virtually every biological system
• Walker directly challenges the common cultural narrative treating minimal sleep as a mark of productivity or toughness, presenting extensive research showing this pattern instead produces measurable, significant cognitive and physical health costs
• This foundational framing, drawing on Walker's own extensive sleep research career, sets up the book's overall project: detailing sleep's specific biological mechanisms and functions, and their measurable degradation under conditions of chronic sleep deprivation

This foundational premise establishes the book's urgent tone throughout, treating widespread sleep deprivation as a genuine, underaddressed public health concern deserving considerably more serious attention than it typically receives in either individual behavior or broader public policy.