Plant phytoalexins are a class of low molecular weight compounds that accumulate in response to biotic and abiotic elicitors such as pathogens, wounding, freezing, UV light, and exposure to agricultural chemicals. Phytoalexins have been identified in at least 75 plants including cruciferous vegetables, soybean, garlic, tomato, rice, beans, and potatoes suggesting plants may be a rich source of cancer-fighting compounds. Preclinical evidence suggests these compounds possess anticancer properties including an inhibition of microbial activity, cell proliferation, invasion and metastasis, hormonal stimulation, and stimulatory effects on expression of metabolizing enzymes. This review highlights the plausible molecular mechanisms through which phytoalexins regulate biological processes that can impinge cancer development. Targets of phytoalexins include signal transduction pathways, transcription factors, cell cycle checkpoints, intrinsic and extrinsic apoptotic pathways, cell invasion and matrix metalloproteinase, nuclear receptors, and the phase II detoxification pathway. Additional research should address physiological relevant dietary concentrations, combinations of phytoalexins and interactions with other dietary compounds, duration of exposure, and tissue specificity as variables that influence the effectiveness of phytoalexins on normal and cancerous processes.