The electromagnetic spectrum is a vital part of our environment. Measures of radio frequency emissions from natural phenomena enable both practical applications, such as weather predictions and studies of the changing of Earth's climate here at home, and reveal the physical properties of cosmic sources. The spectrum is therefore a resource to be used wisely now and to be protected for future generations. Handbook of Frequency Allocations and Spectrum Protection for Scientific Uses: Second Edition sets forth the principles for the allocation and protection of spectral bands for services using the radio spectrum for scientific research. This report describes the radio frequency bands used by scientific services and includes relevant regulatory information and discussion of scientific use of frequency bands. This reference will guide spectrum managers and spectrum regulatory bodies on science issues and serve as a resource to scientists and other spectrum users.