Reading and writing are often taught separately. This article explores the crucial relations between these skills, emphasizing the importance of understanding the "what" and "why" to effectively plan the "how" of integrated reading-writing instruction. The Interactive Dynamic Literacy Model (Kim, "Reading-writing connections: Towards integrative literacy science." Springer; "Journal of Learning Disabilities," 2022, 55, 447), supported by empirical evidence, illustrates how reading and writing skills are interwoven, forming hierarchical, interactive, and dynamic relations, and advocates for integrated teaching to enhance the development of both skills. Understanding these relations is essential for educators to design comprehensive and effective literacy instruction that supports the development of both foundational and higher-order reading and writing skills. We propose three principles for effective integrated reading-writing instruction: (a) leveraging assessment data in reading and writing to inform effective integrated instruction; (b) ensuring the development of lower-order skills while also supporting the development of higher-order skills; and (c) making reading-writing connections visible. Illustrative examples are provided.