Regulatory T-cells are essential components of the immune system, and several different subsets of regulatory T-cells have been described. Considerable regulatory function has been attributed to the CD4+CD25+ T-cell subset. These cells act by suppressing adaptive and possibly innate immune responses thereby maintaining or restoring the balance between immunity and tolerance. The suppressive effects of CD4+CD25+ regulatory T-cells are cell-contact dependent. Recent developments and viewpoints in the field of CD4+CD25+ regulatory T-cells as well as the potential use of regulatory T-cells in immunotherapy of inflammatory diseases are discussed in this volume. By linking data from experimental models with recent findings from the clinic, this book will be of interest to immunologists and other biomedical researchers as well as clinicians interested in the regulation and manipulation of the immune response during inflammatory disease.