This thesis investigates the conventions that shape the subgenre of children's fantasy as they manifest in traditionally published series. As a subgenre of popular fiction, children's fantasy is entrenched in its genre and deeply engaged with the industry that produces it: the inside‚ÄövÑvp textual features and outside‚ÄövÑvp industry features of the subgenre are equally fundamental to understanding children's fantasy. To develop an understanding of the textual and industrial dimensions as they work together to produce genre, I approach children's fantasy through conventions‚ÄövÑvp‚ÄövÑvÆthat is, the knowledges and practices that standardise novels and their production. Conventions enable an exploration of children's fantasy that accounts for both its textual elements and its deep industry connectedness. Drawing on Howard S. Becker's conceptualisation of conventions in art worlds,‚ÄövÑvp I conceive of two distinct kinds of conventions: storytelling conventions‚ÄövÑvp and professional conventions.‚ÄövÑvp Storytelling conventions comprise what we find in books, including the elements of plot, character and setting, as well as style and form. Professional conventions are those that inform perspectives regarding how the industry works, its processes, and the relationships between and behaviours of the people who produce books. My thesis combines textual and paratextual analysis, analysis of book-related media (blogs, websites, published interviews), and primary interviews with participants engaged in the production of children's fantasy to reveal how conventions shape the subgenre and to explicate their functions and effects. The first part of my thesis examines the location of children's fantasy in the broader fiction industry, the professional values and relationships that drive the processes of book production in the subgenre and the storytelling conventions at its centre. Through this analysis, I consider how conventions shape children's fantasy novels, always conceived as both creative works and commercial products. The second part of my thesis comprises case studies that examine specific elements of convention I identify as fundamental to children's fantasy. I discuss conventions as enabling, elastic and reciprocal. These case studies discuss Rick Riordan's multiple sequel series set in the world of Percy Jackson, Holly Black and Cassandra Clare's Magisterium series and Jessica Townsend's Nevermoor series. The concerns of these chapters are character branding, seriality and diversity in the first, creative collaboration in the second, and marketing and success in the third. These three areas of focus enable new insights into the core workings of convention in children's fantasy. The broad aim of this thesis is to enhance understanding of children's fantasy and propose an approach to genres and subgenres of popular fiction that accounts for their multiple facets. In addition to advancing the study of popular fiction, my thesis contributes to the areas of children's fiction and publishing studies. My thesis's findings are relevant to researchers in all three areas, as well as to aspiring authors.