The substances which can cause cancer are known as carcinogens. They can cause damage to the genome or disturb the cellular metabolic processes. A few examples of cancer-causing substances are tobacco smoke, asbestos and dioxins. Carcinogens act by changing the metabolism of the cell or damaging their DNA. This in turn leads to the formation of tumors. The condition wherein the cancer cells move away from the original tumor and enter the lymphatic stream or the blood stream is known as metastasis. It involves the spread of cancer from one part of the body to another. Metastasis can be either treated through systemic therapy or through local therapy. Systemic therapy targets the entire body while local therapy focuses on the part of the body which is affected by cancer. This book discusses the fundamentals as well as modern approaches to the research on cancer-causing substances. Also included herein is a detailed explanation of their relationship to metastasis. This book will prove to be immensely beneficial to students and researchers in this field.