Penumbra, from the Latin paene (almost) and umbra (shadow), can be defined as an intermediate zone of transition between light and shadow. Penumbra is therefore that space, both physical and imaginary, where everything is possible: it is the place of the uncanny, where presence and/or absence can produce wonder or horror. This AD positions this archetype in the contemporary world of architecture, investigating the ways it permeates different expressive forms - from critical theory to architectural drawing, from design and planning to photography. The contributors illustrate and discuss how penumbra has shaped their creativity and modified their approach to the design process. As a physical phenomenon, penumbra has supra-historical and global connotations; nonetheless, different cultures elaborate its symbolism in different ways. Its wide semantic spectrum powerfully inspires creative forms that hover between fullness and emptiness, presence and absence, past and future. The critical perspectives in this issue offer a wide analysis of penumbra's expressive potential and the key to an in-depth understanding of this elusive layer of reality.