In humans, actinic keratosis is the most frequent lesion of the skin initiating a cascade of tumors ending with the squamous cell carcinoma, actinic type. This health problem is increasing worldwide in incidence in the past decades. It is most prevalent in fair-skinned individuals who expose their skin to ultraviolet light from sunshine and artificial sources. The present book provides essential up-to-date information about this common condition. It is presented in a convenient and practical format. This book explains new developments in the understanding of the skin cancer cascade initiated in the field photocarcinogenesis giving rise to actinic keratosis at the source of invasive actinic squamous cell carcinoma and its metastases. Quandaries about nosology, clinical diagnosis, histopathologic assessment, molecular biology advances and management are addressed. This book assembles important new scientific information on all aspects about the skin cancer cascade induced by the environment. It covers the clinical features and epidemiology to support prevention and therapy. Early diagnosis and treatment are essential in the populations at risk. This actinic keratosis survey will be an invaluable reference for all clinical dermatologists and any other physicians and researchers interested in skin cancerology covering the spectrum of chronically sun-exposed skin. The thousand and one facets of actinic keratosis was written to fit the clinical needs of very busy dermatologists, oncologists, skin investigators, pharmacologists, physician assistants and any practitioner caring for patients particularly exposed to a sunny environment.