The Swiss Light Source (SLS) has been operational since 2001. In the last two decades, unique and world-leading scientific programs and methods have developed from the SLS in fields as diverse as macromolecular biology, imaging, and the electronic structure and behaviour of novel and complex materials. These achievements have been largely underpinned by the excellent performance of the electron accelerator and storage ring, which was considered the benchmark in this field until well into the second decade of this century. With the advent of novel technologies in accelerator physics and the consequent emergence of the next generation of storage-ring facilities, known as diffractionlimited storage rings (or DLSRs), it has now become imperative to upgrade the SLS in like manner. The general features of DLSRs, the characteristics of the new SLS 2.0 machine, and the scientific opportunities it will offer are the subject of this in-part didactic article.