Many of the spices and herbs used today have been valued for their antimicrobial effects and medicinal powers in addition to their flavor and fragrance qualities. Most of the foodborne bacterial pathogens examined were sensitive to extracts from plants such as cinnamon, clove, garlic, mustard, onion and oregano. The antimicrobial compounds in spices and herbs are mostly in the essential oil fraction. The Gram-positive bacteria were more sensitive to the antimicrobial compounds in spices than Gram-negative bacteria. The extent of sensitivity varied with the strain and environmental conditions imposed. Certain spices can have a direct effect on the rate of fermentation by stimulating acid production in starter cultures. Phenols, alcohols, aldehydes, ketones, ethers and hydrocarbons have been recognized as major antimicrobial components in spices. The antimicrobial activity and modes of actions of spices and their major antimicrobial components are reviewed.