"Threshold Concepts in Practice brings together fifty researchers from sixteen countries and a wide variety of disciplines to analyse their teaching practice, and the learning experiences of their students, through the lens of the Threshold Concepts Framework. In any discipline, there are certain concepts the jewels in the curriculum whose acquisition is akin to passing through a portal. Learners enter new conceptual (and often affective) territory. Previously inaccessible ways of thinking or practising come into view, without which they cannot progress, and which offer a transformed internal view of subject landscape, or even world view. These conceptual gateways are integrative, exposing the previously hidden interrelatedness of ideas, and are irreversible. However they frequently present troublesome knowledge and are often points at which students become stuck. Difficulty in understanding may leave the learnerin a liminal state of transition, a betwixt and between space of knowing and not knowing, where understanding can approximate to a form of mimicry. Learners navigating such spaces report a sense of uncertainty, ambiguity, paradox, anxiety, even chaos. The liminal space may equally be one of awe and wonderment. Thresholds research identifies these spaces as key transformational points, crucial to the learners development but where they can oscillate and remain for considerable periods. These spaces require not only conceptual but ontological and discursive shifts. This volume, the fourth in a tetralogy on Threshold Concepts, discusses student experiences, and the curriculum interventions of their teachers, in a range of disciplines and professional practices including medicine, law, engineering, architecture and military education. Cover image: Detail from Eve offering the apple to Adam in the Garden of Eden and the serpent c.152025. Lucas Cranach the Elder (14721553). Bridgeman Images. All rights reserved.