Noninvasive imaging of functional and molecular changes in cancer has become an indispensable tool for studying cancer in vivo. Targeting the functional and molecular changes in cancer imaging provides a platform for the in vivo analysis of the mechanisms such as gene expression, signal transduction, biochemical reactions, regulatory pathways, cell trafficking, and drug action underlying cancer noninvasively. The main focus of imaging in cancer is the development of new contrast methods/molecular probes for the early diagnosis and the precise evaluation of therapy response. In clinical setup, imaging modalities facilitate screening, prediction, staging, biopsy and therapy guidance, therapy response, therapy planning, and prognosis of cancer. In this book chapter, we review different established and emerging in vivo imaging modalities and their applications in monitoring functional, molecular, and metabolic changes in cancer.