Passive solar buildings combine energy-saving techniques with natural heating, cooling, and lighting to create comfortable and cost-effective spaces. They use up to 90% less energy than regular buildings. People are interested in this approach because it offers a sustainable alternative to relying heavily on artificial lighting and heating systems. Designers have learned valuable lessons over the past decade and have developed guidelines for incorporating passive solar features into building design. Monitoring of many buildings has shown positive results in terms of energy efficiency. Tools for analyzing designs and ongoing research are available to support this eco-friendly approach.