The fields of cancer immunology and immunotherapy continue to make great strides in providing both a comprehensive understanding of the basic mechanisms underlying tumor-immune system interactions and applying this knowledge to the development of effective immune-based cancer therapies. This Keystone Symposia meeting is organized to highlight recent insights into the complex roles of immune components and pathways in controlling or alternatively promoting cancer and to showcase recent uses of cancer vaccines, checkpoint blocking strategies, adoptive cell therapies and cellular engineering approaches, either as mono- or combinatorial therapies, that have resulted in durable, effective and safe therapeutic responses to an increasing number of cancer patients. Part of the meeting will also focus on new, developing technologies that are likely to expand our capacity to monitor the effects of cancer immunotherapy with a precision, refinement and at a level that has not been possible in the past.