This book presents a novel perspective on immobility, a topic often overlooked in urban planning and transport studies. It argues that conceptualizing, measuring, and analyzing the diverse forms in which individual immobilities manifest can provide crucial insights for designing more inclusive and sustainable planning policies. Immobility is here framed as a relative condition, where individuals experience reduced movement across time and space compared to others. While mobility is often seen as essential for social inclusion, this book challenges the notion that immobility is inherently negative. Instead, it positions immobility as not only the result of specific personal or spatial constraints but also as a reversible, voluntary choice to reduce daily travel. This choice can be influenced by the level of accessibility and proximity to valued spatial opportunities and can yield significant socio-environmental benefits. The book introduces an innovative framework that integrates immobility into urban planning theory and practice. Through case studies, it addresses four main operational challenges to foster a deeper understanding of immobility's social and spatial implications: the measurement of immobility, the analysis of spatial conditions that facilitate chosen immobility, the exploration of the lived experiences of immobility, and the examination of planning policies that can promote reversible immobility to advance social inclusion and sustainability. By examining immobility in both its constrained and reversible forms, the book contributes to broader debates on how to achieve inclusion, sustainability, and accessibility through planning.