The purpose of this qualitative study was to develop a model of instructional design that high school teachers use to promote students' proficiency in 21 st century skills. Although research has led to the development of frameworks of skills that high school graduates should develop during their years of schooling (Lemke et al., 2003; Partnership for 21 st Century Skills, 2007b; Wagner 2008), few, if any, comprehensive theories about designing instruction to promote students' proficiency in 21 st century skills seem to exist. A qualitative methodology using a grounded theory approach was used to gather data and develop the model. Fourteen teachers were recruited from two suburban high schools in Connecticut that were purposefully selected because their district goals or mission statements focused on 21 st century skills. The study was conducted in four phases. The first three phases encompassed recursive stages of interviewing study participants (N = 14), exploring and coding the data, and developing interim data summaries. The fourth phase of the study involved the final analysis and integration of data. The model of instructional design for 21 st century skills that emerged from the iterative analyses of teachers' stories has as its central category an inquiry-based approach to teaching and learning. Further, their accounts of designing instruction yielded the model components: environment, planning, instructing, and assessing students' proficiency in 21 st century skills. The model of instructional design for 21 st century skills presented here most closely resembles Danielson's (2007) framework for teaching, which includes planning and preparation, the classroom environment, instruction, and professional responsibilities. Participants' descriptions of how they designed instruction to promote students' proficiency in 21 st century skills also aligned in many ways with Marzano et al.'s (2001) effective teaching strategies because, as with Marzano et al., participants did not explicitly talk about their planning process, and their methods of assessment were embedded within the instructional strategies they described. Finally, the model expands Skowron's (2006) conceptualization of instructional design in that it moves beyond plan, instruct, and assess by adding the dimension environment, which encompasses technological, emotional, physical, and curricular factors important to nurturing high school students' proficiency in 21 st century skills.