This study explores theories of content literacy and disciplinary literacy in search of implications for reading content development, building on the reading competency concept and assessment framework of the Programme for International Student Assessment (PISA) 2018 that reflects the orientation of literacy education in the 21st century. Common Core State Standards(CCSS) emphasized literacy education, focusing on close reading, complex texts, and multiple-document reading. The effects of generic literacy skills have been widely questioned by secondary subject teachers. A new disciplinary literacy theory asserts the need to balance content and literacy, going so far as to suggest unique literacy skills for subject content. PISA trends and advanced literacy instruction in disciplinary literacy theory, underlying readers’ roles and goals and authentic reading tasks, suggest models for content-area reading and content literacy instruction. In Korea, the psychological approach to reading competency, which still adheres to the 2015 curriculum and textbooks, should be converted to a social constructivist perspective and text-based reading tasks with multiple documents. To do so requires empirical studies for reading task development based on collaboration between disciplinary specialists and literacy experts.