Intensive care is one of the largest, most expensive, and complex components of U.S. health care. Errors and the resulting adverse events are, however, common in intensive care units (ICUs). Theories about errors in high-risk environments, developed by aviation and other industries, provide insight into why ICUs are prone to errors. Complex systems--of which ICUs are certainly an example--are breeding grounds for errors because interdependent components interact in unexpected ways. To achieve favorable outcomes, ICUs require that many processes occur in sequence. For example, patients are cared for by many providers with varying levels of expertise across several disciplines, and these providers use highly sensitive and potentially dangerous technologies and medications. Such complex systems require careful planning, excellent teamwork and communication, and designed redundancies to recheck for proper care processes. This paper provides a practical framework for improving patient safety.