This article proposes a new research approach to teachers' lesson planning. While numerous guidelines have been dominating lesson planning as an object of teacher education, we utilize teacher cognition and expertise research to view lesson planning from a different perspective: We argue that lesson planning typically demands specific cognitive skills that teachers must master to create high quality instructional practice. The so-called CODE-PLAN model ("co"gnitive "de"mands of lesson "plan"ning) forms the general theoretical framework for our conceptualization of six demands (content transformation, task creation, adaptation to student learning dispositions, clarity of learning objectives, unit contextualization, and phasing) to empirically describe and analyze teachers' planning competence. We investigate how these demands are met through content analysis of 337 plans for demonstration lessons written by teacher candidates during induction in Germany. Statistical findings on the construct, curricular, and predictive validity of planning competence measures show that the CODE-PLAN model may open new empirical research perspectives on teacher planning competence and stimulate curriculum design in teacher education.