The past decade has been marked by rapid advances in molecular biology techniques, which are now routinely and commercially available for research groups around the world. Examples include the microarray technique and methods for gene silencing such as small interference RNA (siRNA) and cell transfection with antisense constructs. For research groups interested in the pathogenesis of certain diseases, these novel techniques allow a rapid high throughput screening for genes which are differentially expressed in health and disease, and might thus be of functional importance for disease development or disease progression [1]. In this context, there has been major progress in our understanding of the pathophysiology of connective tissue diseases. Connective tissue diseases form a wide spectrum of disorders including, among others, systemic lupus erythematosus, systemic sclerosis, dermato-polymyositis, mixed connective tissue disease and Sjogren’s syndrome. The pathophysiology and clinical presentation of these diseases are diverse. However, the discovery of key molecules as well as key mechanisms in the specific pathogenesis have significantly increased the options to treat their organ-based complications. While the conventional non-selective therapies are still of importance in daily clinical life, most of the new agents target specific molecules or mechanisms that have been shown to play a functional role in the pathogenesis of the overall disease or certain organ manifestations [2, 3]. To provide a comprehensive background for these new therapeutic options and to summarize novel developments, this supplement of Rheumatology has gathered experts in the fields of rheumatology, dermatology and nephrology to cover different aspects in the epidemiology, pathophysiology, clinical features and their pathophysiology, and treatment of patients with connective tissue diseases. Regarding epidemiology, it is shown in this supplement that the incidence and prevalence of connective tissue diseases are low compared with other inflammatory rheumatic diseases such as rheumatoid arthritis or spondarthropathies; however, they are potentially life-threatening. As connective tissue diseases often occur in younger women during the childbearing period, treatment and clinical care during pregnancy is a major challenge for clinicians. Classification criteria used in clinical studies to obtain well-defined study populations frequently underestimate the prevalence of the disease by excluding patients with early disease or incomplete disease manifestations. Since novel