The chapter deals with papulosquamous disorders. Papulo means papules and squamous means scale. These diseases have papules or plaques with scales. Psoriasis is an itchy, chronic, recurrent, immune-mediated, inflammatory inherited disease. Pathology, triggering factors, types, histopathology and treatment protocol of psoriasis are defined. Auspitz sign is the clinical reflection of elongated vessels in the dermal papillae together with thinning of the suprapapillary epidermis. Lichen planus is an autoimmune, inflammatory disease of skin, mucosa and hair follicles. Reactive arthritis or Reiter’s disease is a classical triad of arthritis, urethritis and conjunctivitis. In pityriasis rubra pilaris, red follicular hyperkeratotic papules occur. Seborrheic dermatitis causes erythematous scaly patches of sebaceous glands.