The immune system mounts a well-orchestrated response to tumors. However, despite this response, tumors are able to grow and evade immune recognition. This chapter reviews the mechanisms involved in the immune response to tumors and introduces the concept of the cancer immunity cycle. It continues by describing the mechanisms that tumors utilize to circumvent immune recognition that ultimately lead to tumor progression. Understanding these mechanisms has led to the development of immune therapies for the treatment of cancer. This chapter concludes by discussing the current immune therapies utilized by physicians in the clinic for the treatment of cancer patients.