Psoriasis is a non-communicable and chronic autoimmune disease. It is characterized by red, itchy scaly patches mostly on the knees, elbows, back and scalp. There are five main forms of psoriasis. It includes plaque psoriasis, guttate psoriasis, inverse psoriasis, pustular psoriasis, and erythrodermic psoriasis. It is a genetic disease, which is stimulated by environmental factors. Stress, obesity, smoking, alcohol consumption, skin dryness, HIV infection, and certain drugs are some key factors that prompt this condition. It leads to several complications such as conjunctivitis, metabolic syndrome, Crohn's disease, Parkinson's disease, etc. Diagnosis varies according to the appearance of the skin. It includes differential diagnosis and in certain cases a skin biopsy. Psoriatic arthritis is a type of inflammatory arthritis which affects people who have psoriasis. The most common treatments for mild to moderate psoriasis include topical treatments (application of creams or ointments), phototherapy, and systemic treatment (oral and injected medications). Treatment of psoriatic arthritis involves biological therapies, non-steroidal anti-inflammatory drugs and steroid injections. From theories to research to practical applications, case studies related to various topics of relevance to psoriasis and psoriatic arthritis have been included in this book. Students, immunologists, doctors, researchers, and all interested in this medical condition will find it beneficial.