The interactions among cells, structural and other proteins, and large and small molecules in the dermis is an extremely complex, and largely unknown subject in normal skin, so that these interactions in wounded skin are incapable of complete comprehension at present. The problem is compounded by the further reaction and interaction of formed structures within the dermis, such as blood and lymphatic vessels and nerves of all types, and adnexal structures, as well as interactions with the epidermis, which are separately reviewed in the following chapter. In spite of all of this, there are several areas in which research has provided rather extensive insight into the wound healing process. These areas will now be reviewed. A separate review has been provided in this volume of the results obtained using in vitro systems for studies of the wound healing process (Chapter 6). Wound healing has been traditionally divided into three phases: (1) the inflammatory phase, also known as the exudative, lag, or substrate phase; (2) the fibroblastic phase, also known as the connective tissue or proliferative phase; and (3) the remodeling phase, also known as the resorptive or differentiating phase. Although these phases are somewhat arbitrary, we will use them to organize our approach to the problem, dividing our discussion into the inflammatory phase-to which we shall give emphasis-and later developments. Various aspects of the phases of wound healing overlap extensively.