Secondary osteoporosis is failure of bone mass to develop in the growing skeleton, or loss of bone mass in the immature or adult skeleton, primarily due to reduced mechanical loading arising as a consequence of disease or injury. The condition can be either localised or systemic, depending upon the nature of the underlying disease or injury. Guidance on techniques used in the assessment of bone mass or quality are provided in Chapter 6. The basic biological mechanisms that underlie bone mass and quality attained and the physiological background to loss are discussed in Chapter 3. The study of secondary osteoporosis in paleopathology can help us to understand the effects or consequences, of disease or injury in terms of reduced mobility and activity and experiences leading up to death, in past communities. A series of bullet points are used to summarise the core concepts covered.