This document provides an introduction to designing your day. It discusses managing time and energy as key constraints when designing a productive day. Having enough time is important, but energy levels fluctuate throughout the day and need to be considered. Breaks, exercise, sleep, nutrition and holidays can help maintain energy. The document also discusses the rise of knowledge workers and tools for organizing the day like lists, calendars and prioritizing tasks. Designing an effective day requires considering both time and energy constraints.