Background: To prepare engineers who can address complex sociotechnical problems, a deep understanding of engineers' complex problem-solving approaches is needed. Purpose/Hypothesis: This study operationalizes comprehensive systems thinking as an analysis framework that attends to aspects of engineering work and relationships among those aspects. Leveraging this framework to analyze engineers' complex problem-solving approaches enables attention to social and technical dimensions. Design/Method: We interviewed 46 engineers about their specific complex problem-solving experiences. To explore a range of perspectives, we purposely sampled participants with varying academic, professional, and personal backgrounds and experiences. Data analysis focused on operationalizing comprehensive systems thinking; we first developed a set of aspects that captured the variety of considerations that participants discussed in their descriptions of solving a complex problem. We then inductively developed a scoring guide to differentiate response quality. Results: The scoring approach differentiated the quality of consideration based on a combination of the number of details provided, the degree of specificity, and analytical depth. While most participants discussed the consideration of a wide range of aspects of engineering work, they discussed far fewer possible relationships between these aspects. Contextual aspects of engineering work were consistently the least commonly identified and least likely to be considered in relation to other aspects of a given problem. Conclusions: Our differentiation of various complex problem-solving approaches can guide the development of educational interventions and tools, ultimately facilitating more comprehensive consideration of aspects--and in particular relationships among aspects--and setting up engineers to be more successful at developing appropriate solutions.