The incidence of most cancers increases with age. Cancer is the second most common cause of death in older adults after cardiovascular disease. Many common cancers in older adults can be prevented from occurring or can be identified at an early stage and treated effectively. The prevention and identification of cancer in its early stages, in an attempt to reduce discomfort and disability associated with advanced cancer and cancer treatment, is also a priority. Overscreening for cancer in older adults can lead to unnecessary diagnostic testing and unnecessary treatment. Both older adults and their healthcare providers need guidance on the appropriate use of cancer prevention and screening interventions. This first of a two-part review addresses special considerations regarding cancer prevention for adults aged 65 and older. Screening decisions and the impact of limited life expectancy and an older adult's ability to tolerate cancer treatment are also addressed. Guidance is provided regarding the prevention and early identification of lung, colorectal, bladder, and kidney cancer in older adults. The prevention of breast, prostate, and female urogenital cancers are addressed in Part 2. J Am Geriatr Soc 68:2399-2406, 2020.