The Cruciferae (also known as the Brassicaceae) are the family of plants that include the various familiar members of the species Brassica oleracea (e.g., broccoli, cabbage, cauliflower, kale, Brussels sprouts) as well as many other plants that are widely consumed in various parts of the world. Forage and root brassicas are widely used as winter feeds for cattle and sheep. A striking and characteristic chemical property of cruciferous plants is their high content of glucosinolates (more than 120 types), which often approaches 1% or more of their dry weight. The interest devoted to this group of natural products is caused by the appreciable biological effects of both the intact glucosinolates (GSLs) and especially the complex group of glucosinolate transformation products produced in non-enzymatic and enzymatic reactions. Depending on the concentration and structural types of these compounds, their biological effects can be toxic, antinutritional or beneficial to health. Most serious economic problems in livestock seem to result from rapeseed meal; arising from GSLs or their breakdown products. In contrast, GSLs and their isothiocyanate (ITC) hydrolysis products are reportedly well-known protectors against carcinogenesis. GSLs play further protective and evolutionarily important roles in plants. These include allelopathy (suppression of growth of neighboring plants), specific positive and negative feeding cues for some insects and broad antibiotic properties including nematocidal, antimicrobial, antifungal, antiprotozoal and insecticidal activities. The controversy in the referred actions contributed to crucifers' phytochemicals has been exclusively discussed.