Biological aging is a fundamental process observed in almost all living beings. It is characterized by a progressive impairment of biological systems leading to an increase in age-related mortality. The understanding of the mechanisms of aging is of particular interest not only from a general point of view, but it has wide implications for both the human individual and society. Specifically, understanding the basic mechanisms leading to human aging will certainly provide novel strategies to deal with the many different and severe age-related diseases (e.g., different types of cancer, Alzheimer's disease, cardiovascular diseases) and can be expected to increase the quality of life in old age significantly. Despite this obvious significance, it is amazing how little is known about the basis of aging. Currently, it is not clear whether there exists a single conserved mechanism by which all biological systems age, nor is it clear whether or not such a mechanism accounts for aging in a single species. However, beside these and many other open issues, it is clear today that there is a genetic component of aging. It is also clear that age-dependent changes of genetic information play an important role. The processes leading to the observed age-related accumulation of DNA alterations is dependent on two major factors: the rate at which the alterations occur and the ability of the biological system to repair them. In addition, there are a number of different types of DNA alterations known. One group of changes are unspecific and occur randomly. Other alterations result from the differential activity of specific genetic traits (e.g., age-related genes, mobile genetic elements). Moreover, DNA changes may be subtle, occurring at the nucleotide level, or may include larger regions of the genetic information. In this review we focus on the latter type of age-related DNA reorganizations. We will refer to reorganizations which are of special relevance in different biological systems.