Despite numerous papers and books published each year, natural products from Algerian flora are poorly explored. This book intends to make the reader familiar with all aspects of Essential oils and other plant extracts with a historical perspective, sources and chemical analysis and processing. The experimental part aims to focus on Lamiaceae family by studying the chemical composition of essential oils and crude extracts of two representative genders: Lavandula and Rosmarinus. The last chapter exhibits the biological potential of studied products to replacing chemical toxic substances utilized as food preservatives.